Congratulations on getting one. Diomedes gave you a list of retail games to get I'll give you a list of downloadable games:
Mortal Kombat II (Online), Tekken 5: Dark Ressurection, Gripshift, Calling All Cars, Crash Bandicoot, Flow (if you like 'different' games), Super Rub a Dub (if you have kids)...
Also get the folding@Home thing and help science and humanity damn you!
Thanks to Blacksaber for the sig!