If you don't have one, I'd go with a 42" LCD TV. (size may be off due to price estimates).
If you already have a really nice TV, I'd go with a Blu-Ray player/PS3 (I know you said no other console, but it is a cheap Blu-Ray player).
I wouldn't buy a surround sound system, because a good system with decent speakers will run you a few thousand which you obviously aren't spending that much. The home theaters in a box are junk and a waste of money unless you really don't care about the sound quality. In which case, why even buy a surround system.
If you aren't interested in that and hate having multiple controllers you could go with the Logitech Harmony 890/900/1000/1100 Universal RF remote. I have the 890 and I love it. I can control all my devices from anywhere in my house.
If you live by yourself and your 24yo your place probably isn't the cleanest it could be. Get a Roomba, I want one myself, but haven't gotten around to buying it 
EDIT: lol, I started typing when you only had like 5 responses. See what happens when you get pulled away from your PC 
EDIT 2: I don't buy Blu-Ray movies either cause I think they are too expensive, which is why I use Netflix for $15/month I get unlimited DVD/Blu-Ray rentals. I probably pay around $1.50 per rental which is really cheap. I don't know if you have any comparable services over there.
