You can throw anything at them, if you make the means available to defeat it.  You have Storyteller block?
See if this helps get any creative juices flowing.  http://en.wikipedia.org/wiki/List_of_legendary_creatures

Just randomly picking one from the A's - Agathodaemon (Greek) - Spirit of vinefields and grainfields.
You mentioned that the setting was at a college campus.  I immediately see the spirit causing problems because of something going on at a local vineyard, and it involves the Players via an on campus wine tasting/party/drinking binge/whatever.

I enjoy non-challenging encounters.  Players tend to over think them and miss the subtle points you are throwing at them, plus it adds a little comfort and trust in the players abilities.

For instance:  My players once got pulled over by a sheriff of a small town on the drive back to Dallas.  The Van they were driving was smoking badly and sputtering. (compel on the wizard because of his aura).  Insert easy Social Conflict.  The officer takes time to do a couple of navel gazing actions and applies some temp aspects on himself.  "respect the badge" and "I am the law".  Once his hat is straight he approaches the Van.  The players assume, the officer is simply wanting safe vehicles on the road, and will question them about it.  A few rolls later the players win the trust of the officer and avoid a ticket.  As the scene is ending.  The van won't start.  Stranding the party in the small town while they wait for the Van to be fixed.    Cue social conflict #2.  The tow truck driver/mechanic.  He wants to over charge the city slickers and make some easy money.  The players again win the social conflict and talk him down to minimal repairs and set a 1 day time frame.

What do these have to do with anything?  They are means of easy player challenges that move the plot forward, and keep them involved.  Not to mention encourage both role playing and roll playing.  Plus it allowed me as the GM to introduce the BBEG to the players without them even suspecting a thing.  The sheriff is behind events that will unfold on the day the players are stranded in town.  He has seen faces, knows player names, and is saavy enough to identify a threat to his plans when he sees it.  Now the mysterious ambush at the hotel, the abduction of a player, and other events makes a little more sense in the end.  Not to mention the Scooby Do moment when the BBEG is revealed and the players all go, "Sheriff Withers!" *gasp*  And he would have gotten away with it too!

To sum up, I agree with the line "Not every encounter should be an all out fight against superior forces that require every tool just to survive."  I am a big fan of plot twist, and thinking your way out of situations.

One shots are hard.  Time is always a factor.  You never know how many tangents will come up.  Plus you have to linearize the adventure to an extent the players understand quickly what they need to do, and don't derail themselves for too long making plans.

My suggestions would be:

Start with a strong transparent hook. 
Something that would draw all or part of the players in, and would motivate them to temporarily leave the main story line to pursue the new story side line, because they know it will be quick and they can see what they need to do.

Only have a few scenes.
Keep it simple you only have a few hours.  Come up with a few scenes and leave it at that you are working with a small temporal window.

Try to limit it to 1 or 2  combats.
I don't know why but combat tends to slow most groups down.  Strategy talk, past glory tangents, map drawing, figure moving.  I don't understand how that could possible occur, but it does.  (Yes I understand why it happens.)  Use it to your advantage.

Quick off the top of my head examples.

While stopping for gas and snacks going to (insert storyline proper location).  The group gets caught up in a gas station robbery, a local gang has swung in for beer and smokes, they are armed and in the mood for a fight.  I can envision a firefight scene with things exploding off the shelves, coolers getting shattered, chips and soda spraying everywhere.  Perhaps one of the gang members is talking crazy yelling about what he sees.  They flee, party pursues.  Final showdown at gang house, where the party discovers the crazy gang member was high on third eye, and you have a future hook to bring down a supplier.  After something like that your players will remember the one shot every time they walk into a Quick Stop gas station.

Or how about . . .
Gun shots in the neighborhood lead them to a woman who just shot her husband and is running from the scene.  When they ask her what is going on, she is all emotional crying, he just wouldn't stop, I had to.  You get the weapon away from her, and calm her down.  Then her husband shows up.  Two gun shot wounds and all it did was piss him off.  Insert supernatural monster here, and reason.

What about . . .
Its memorial day, and all the people that have been visiting graves are acting funny.  Players discover this when one of them visits a family grave.  A local necromancer has set up ritual traps to allow the dearly departed to temporarily possess a family member that brings gravestone decor.  All kinds of confusion, and man out of time jokes available.

Hope this helps,
BaH

I like this a lot.  I can see some home brew random charts filtering through my mind as I type.

Hasn't anyone else had the game slow to a crawl when someone wants to bust out a ritual to fix something? I'd say do whatever you can to pick up the pace so you can focus on the story. Like I said before if he can't fail (or won't fail as is the case) then there's no reason to go through all however many rolls. It's one of the basic tenants of gaming. If nothing will happen if someone fails (or there's no reason to expect them to fail) then there's no reason to roll. Just make sure you properly represent the time taken to make it in game and move on.

Game Time/Advancing the Plot/Rolling Dice . . . it is all situational.  I ask myself some questions.
Q: What are the other players doing? Could any of it be distracting? 
A: Nothing/No (next question)  Arguing/Yes (Better roll you just got some negatives.  Nope not gonna tell you.  Okay you succeed, but it was close.  Compel a temper flare, wizards trying to work and all.)

Q: What could the other players accomplish while the Ritualist is making his mini-nuke?
A: Nothing (speed up the process - next scene)  Otherwise, let the wizard do his thing, players are doing their's.

My 2cents,
Bubba Amon Hotep

Had a person who wanted to be a knight of the cross in a game I was running.  I let them do it based on backstory.  The father used a blade, she trained growing up to wield it.  And is passing it down to her.

Then added my own underlying twist, and the relation to this topic. You see her father was a cultist who used the black.  The cult over the ages had gathered fragments from THE cat-o-nine tails used to give Jesus his lashings.  Since Lucifer had tainted it, by compelling the guards to torture him, the sword forged from the Cat-o-nine tails was also dark.

The player attempted to be a knight of the cross with the dark sword, but little accidents/coincidences would corrupt her efforts.  Later she found out about the sword, brought down the cultists one by one, including her father, and sought out a sympathetic Wizard (Harry) to help destroy the blade.

The real Knights get involved, and through her prior actions, and during a baptism of sorts, the blade is cleansed.  The player enjoyed it, and that is the first rule of the game.  HAVE FUN.

I believe there was an old Indiana Jones adventure based on the 4th nail.  And how it relates to traveling gypsies.

Weird Character Combinations:

1) Emissary of a Dragon - Problem solver for the big "boss".  A mainly social character who can get physical via powers.  Doesn't like to start drama, but will settle things if provoked.  Travels the world doing jobs for the "boss".
2) Focused Practitioner - A wizard want-to-be on the run from White Court, Red Court, and Black Court. Always moving as to never put down roots, and stay on the run. Distrusts everyone.
3) Wolf-were - A wolf who learned to shape shift human. Doesn't understand human culture. Distrusts everyone. Roams like a gypsy.
4) White Court Virgin - Hidden by her mother as to not grow up "In house", she learned to feed off Adrenaline and travels with a carnival.  Thus never staying in one city long.  Distrusts everyone.

As GM I find this a Weird group, because they are all women. (I'm a guy).  They all wander, so no one city will work to contain them, and they distrust each other and rather split up and do things solo.   Its always difficult running 4 adventures around the table at the same time, and trying to cross them over so the characters can interact.  Hopefully after the latest cross over I have planned they will TRUST each other with their lives.

Speaking of the spear of destiny.  It is suppose to have a nail from the cross on it.  Which can't be so in the dresdenverse.  However the original metal head of the spearhead could still be around.  Whereas it wouldn't have been Soaked in Blood as long as the nails, it would still I think garnish power.  Besides the fact that so many people believe in it.  Of course aren't their like 3 spears in various museums around the world claiming to the be "the one"? (Maybe they all are a single piece of a 3 piece whole)

Along that line of thought, Before the Dresden RPG, I was running a Dresden game with the Witchcraft system.  I had a "knight want-to-be character" but couldn't justify giving them one of the "true swords" so I came up with a minor sword theory. based on the metal, ceramic, bone pieces that had been tied to the Cat-O-Nine Tails used to torture Christ.  They had been gathered by a group, and placed in the pommels of 9 swords.  They acted like the Swords of the Cross but on a much smaller scale.