If you like the civ games, there's also Civilization: Colonization, which you should be able to find for less than 30$. Basically it's Civ that is more focused on the trade aspect. You land in the new world and start building Civ style gaining resources, which you can convert to goods, making treaties with the natives and other settlers. Only you're still connected to the king in england, who basically acts like an asshole to you (taxes, ring kissing ect.) till you decide to have a revolution. At that point the game turns in to a survival war game where you're fighting off constant invasions from the motherland.
Depending on what exactly you liked the most about KOTOR/Oblivion, mass effect/fallout would be good for you. I really liked both, but both had the problem of having side quests that were kind of repetitive. (Although fallouts side quests were significantly less repetitive than the constant random planet landing in mass effect.) Fallout could really just be a mod of Oblivion with a hybrid turn based combat system added in. Mass Effect could be Kotor with a less turn based hybrid combat system added in.
The zombie shooting game (left4dead) is pretty fun if you can find people to play with. But as it is now there are only 4 maps to play.