Baldur's gate plus BG 2 and the expansions were great, it is amazing how they made pretty much the same game 4 times but still very differntly, all are highly replayable.

You can take differnt paths, try it with a team of six or try and do a simple Warrior/cleric combo.

 

A old game I have just started playing again, Wing Commander: privateer. Epic game, graphics were amazing for the day and even passable for today. Endless fun. And like many old games you can download it free online.

 

I recently started replaying some of the MechWarrior games and they're still surprisingly fun. Better yet, MW4 is coming out as a free download sometime soon and they're in the process of making MW5.