Swords and Soldiers HD
Hydrophobia is on sale for a day and looked neat, but I haven't played it.
VVVVVV
World of Goo
Mini Ninjas
If you like Point and Click Adventures (like Monkey Island) you might enjoy
Jolly Rover. Even if it is pretty much Monkey Island with dogs.
You should also be able to run all the Half Life 2 games.
Eufloria is neat too.
And I enjoyed
A.R.E.S.
That's what I've got after looking over my Steam Library. Check to see if there are multi-game packs or for sales before you leave too. Anyway, have fun while you're gone.