A pair of jeans and some socks.
Don't laugh! I really needed new jeans.
Three weeks ago I also finally upgraded my 4 year old PC, I guess that's the biggest present I got for myself this year.
Went from an overclocked Core2Duo E8400 w. 4GB RAM to the following;
i5-3470, 16GB of DDR3, a micro-ATX case and micro-ATX mobo (Z77-based).
I also got one of those closed radiator/heatsink things from Corsair, a H60.
Kinda looks like this, although this isn't my comp per se:
Compared to my P182 there are 4 less fans fans, better sound insulation and more openings "plugged" on this case (Fractal Define Mini), so it's a helluva lot quiter and nicer to use than the old one.
I'm very pleased with this build, kinda cheap too since I reused the modular PSU (again) and the graphics card (ATi 6870) from the old comp.
Oh, and the Samsung 830 128GB SSD is mad fast to load programs, with the low access times and high burst read speed. I'll never buy a comp without SSD again, very high performance boost right there.