I've run campaigns using Eden's Witchcraft in the past.  I like the system, and the default campaign is close enough to the Dresden-verse that it should be easy to modify.

Also, you can download the core book from Eden Studios' website if you wanted to give it a lookover:
http://www.edenstudios.net/witchcraft/index.html

I expect I'll be robbing ideas from my Witchcraft material if I do end up running a Dresden campaign.

My group and I also have an ongoing D20 Call of Cthulhu campaign currently, and it's turned out fairly Dresden-like, and the D20 Urban Arcana setting would work even better I expect; but I'd still recommend having a look at Witchcraft, even if only for ideas.