2D single player B2P games?

[Mime Taxidermy]

Super Meat Boy?

[Orpheus]

Terraria? Keeps getting updated quite often which is a plus.

[Arri]

Could give Divine Divinity and Beyond Divinity a try, I suppose. They're kinda diabloish games, but with an actual story attached. Should be able to find them for about $10 at www.gog.com or some other site.