Comment Re:The questions developers ask (Score 5, Informative) 249
The Sims, Sims 2, Sims 3...
Elder Scrolls Series
Starcraft
Halflife series
Portal 2 (added a mod tool to stir new sales about a month ago)
Civilization series
Torchlight series
World of Warcraft (heck, almost all MMO's for that matter)