Crassmaster: Others have already done a great job reviewing Arkham Horror, so I'll leave that.
As for a 2-3 player game...did you have any other specific requirements? Do you want somethng co-operative or competitive, for example?
XYCat: It doesn't really matter if it's cooperative or competitive, it's just that i don't expect to find too many board game enthusiasts among my friends so pretty much anything would do as long as it doesn't require too many players.
Well, Arkham Horror is really good IF people are willing to sit and play something for awhile, and if you have room to spread the game out on. Same goes for
Runewars. Think a sort of Masters of Magic lite in board game form.
I can't recommend [url=http://boardgamegeek.com/boardgame/2653/survive-escape-from-atlantis! Escape From Atlantis]Survive! Escape From Atlantis[/url] enough as a simple, fun up to 4 player game with a bit of strategy and a lot of pure evil.
Nexus Ops is a nice little 'dudes on a map' type game (think Risk and such) that plays fast because it's all about offense...no turtling.
Wiz War and
Dungeonquest are both fun, over the top (in a good way) competitive games. Wiz War is a battle between 2-4 players using randomly drawn spell cards. DQ is a gsme with 1-4 trying to escape the dungeon with the most gold. People have run a stat analysis of it and found someone survives less than a third of the time.
Small World is a simple enough territory control game with a random mix of races and abilities every time you play. It has different boards to let 2-5 play at a time and several good little faction expansions available.
If you're in to zombies, check out
Last Night on Earth. If you prefer martians, check out
Invasion from Outer Space by the same company. they also produce
Conquest of Planet Earth, where up to 4 players compete to be the ones to conquer the humans (you could play co-op...but why?). Finally, they ALSO have the monstrosity known as
Fortune & Glory. Think Indiana Jones style pulp action. It's a lot of fun, but it also takes considerably longer to play than any of their other 3 games.
Finally,
Claustrophobia. It's basically a dungeon crawler, but the fight is between post apocalypse humans and demons from Hell. 2 player only but it's very well done and the quality of everything in the box is astounding. A nice expansion and plenty of free downloadable scenarios available from the designer, too.
Let me know which of those looks interesting and maybe I can come up with more based on that.