I saw the TV show first.  I considered it "ok," and was mildly disappointed that it had such a short run.  Honestly, though, it didn't seem particularly "special" to me.  Then sometime later (a few months to a couple of years - can't remember for sure) I was dredging around on Barnes and Noble looking for a new read and stumbled across the books.  I decided that I should at least read the first one, and dove into it without particularly high expectations.

Needless to say, I was gobsmacked.  I thought Storm Front was quite good, and kept reading.  My general opinion is that the first few books are fairly high-end fare, and as I read #7 I was constantly pausing to marvel over what a wild dose of fun it was.  Then #8 just blew me away - that was the one that made me realize I was reading epic fiction.  I think that's the story that made Harry Dresden more than just a character for me, in an extraordinarily deep way.

I might have tried the series out even without having seen the show, but I don't know for sure - there are so many books out there and so many of them are lame.  I remember having a generally discouraged feeling about my chances of finding something good that evening I was searching.  So so glad I tried the series out.  :-)