Well if you liked Limbo, I'd say you need to play Braid. It has far more clever puzzles, interesting mechanics and a lovely, calming atmosphere. Its really the game that got me into indies in general and it stands up today as one of the best still.

Minecraft is probably my favourite indie game, if I had to pick one. Its Legos meets I Am Legend meets The Descent and is one of the most addictive and charming games of all-time. Its not for everybody, though.

The Swapper is another *must-play* game if you like Limbo as well. Like Braid, it has interesting mechanics, clever puzzles and a great atmosphere.

And I second the notion of Brothers: A Tale of Two Brothers. Its gorgeous and fun, short and sweet, never outstaying its welcome.