What systems you got?
All prices mentioned are taken from Steam
For PC (since you mentioned portal):
Doom 3- Good shooter, pretty scary to me, also an excellent modding scene:
http://www.moddb.com/mods?filter=t&kw=Search+...&released=1&style=def&theme=def&game=33&type=def
(plus there's a Hello-Kitty! flashlight mod) 20$
Mass Effect- 3rd person RPG. It's a bioware game, so interesting story and great characterization are a given. Biotic powers are a blast 20$
Fallout 3 - 3rd or 1st person shooter, also an RPG. Wide open world, lots of crap to do in it. 30 $
Fallout 2 - Isometric view, turn based RPG. Doesn't get much better 10$
Psychonauts - 3rd person platformer, fun gameplay and puzzles, cute and funny dialogue 10$
Torchlight - Shameless Diablo 2 ripoff. Still cute though, lots of great mods 20$
World of Goo - Basically, a physics simulator to make puzzles with. Adorable, and honestly thought-provoking. Side effects may include making you a more complete person 20$
Vampire the Masquerade: Bloodlines - You're a blood thirsty, ass-kicking vampire with magical powers, including but not limited to: Transforming in a Wolf-Death Machine Hybrid, Mind Control, Invisibility, attacking people with flocks of Ravens, making groups of people within a certain radius blood implode from the inside, and SO MUCH MORE. 3rd person RPG, loads of replay value, and great mod scene. 20$
Hope this helps. Also hope that you have a pc, or I'm going to be annoyed I spent 5 minutes putting effort into this.