Thanks for all the suggestions! So far it seems like I should get him the chair, with me in a bow and a dance.
I asked another friend and he was leaning towards the stereo because he thought my b/f would think of me more when using it.

I'd love to do the surprise that xcopx recommended, but I can find the stereo he wants pretty cheap online. Kinda ruins the whole pick-it out factor. Best Buy is marking up the one he wants about $100!!!