AR-15 carbine. Actually, an AR-15 lower, and then I'll probably buy multiple upper receivers, barrels, and stocks so that I can have M4, M16A2, M16A4, and XM177 look-a-likes, depending on my mood.
But right now, I mostly want an M4 look-a-like.
After that, I probably won't be purchasing anything else for the rest of the year. I'm back in school right now and don't have a job, so I can't afford to buy guns regularly. Ideally, I'd like a 1911 and some type of pistol for conceal-carry, but I'm probably going to wait a while. Plus, I'm half-expecting that I'll have to move to DC after I finish my Master's, since that's where the work in my field is concentrated. In which case, no more guns for me, ever.