Re: Burn Shift or Dresden Files
Fate Core is free, and pretty easy to learn and pick up the rules. The main thing about it is that it uses a lot of storytelling/creative writing (which lends itself well to pbp, imo).
Dresden Files RPG has a lot of tweaks from Fate core, though, so you'd probably need to get a copy of it (Your Story is the only book you'd need) to be able to play, unless you want a pure mortal character.
Well, now that makes 3 players for DFRPG, if any GMs are interested in picking it up.