I'm a big fan of the OptimalWorkshop suite, especially OptimalSort (online card sorting) and TreeJack (online tree testing of the non-arboreal kind).
UsabilityHub for running remote usability tests, impression test and split testing designs.
An older version of Silverback on my laptop when running usability tests (new version coming soon, they say).
When testing hand-sketched clickable prototypes, I like using Marvel. Just take a photo of the sketches and add hotspots and head off to find a test participant.
UserTesting.com is handy for recruiting remote participants and getting video recordings of them completing specific tasks or UI flows.
I know whatusersdo.com is fantastic too, and keep meaning to use it more.