Plants vs Zombies is hardly an indie game. PopCap is a very mainstream company.
Since you said "no Minecraft" (because too famous now?) I'll go with
Crayon Physics. On a tablet PC with a pen: amazing. Works fine with a mouse too.
It's my favourite because it's unique, simple, relaxing, replayable in multiple ways, and allows for lots creativity and messing around. Hey, just like Minecraft! ;)