Next car is likely a 2008-2009 C-class later this year/early next year, but that's for the wife.
After that it will be my turn, and I'll probably be in the $25k bracket in 3 years or so. You can get a lot of car for $25k.
I'd be looking at (all used, a few years old):
--370Z
--G37 Coupe
--3 series coupe
--Z4 (bit of a stretch, would have to be a 2009+ for the retractable hardtop for winter, not going to put a soft top through winter)
--A5 coupe (hard to say where the prices will be given how new they are, but probably a stretch as much if not more than the Z4)
--Challenger R/T
--Mustang (2011+ with the 5.0)
Although, I'd feel quite bad using a Challenger/Mustang as a year-round daily driver; doesn't feel right to put a muscle car through salt/daily driving (not worried about the power level and fat tires, have only ever had rear wheel drive anyway, feels safer in the snow/ice IMO), more designed to be a weekend summer toy really. The other thing is that I've had two BMWs out of warranty, and that's not really somewhere I'd like to go again. I'd rather not go there with the C-class, but it's what the wife likes so if we can get a low mile one that's certified, maybe we will be ok for a while).
My next toy though, will be a '68 Charger R/T, possibly even with a real-deal Hemi if the cards play out.