Firefly, first and foremost.
Now and Again, if anyone's ever heard of it.
Arrested Development, though it looks like that wish is finally coming true.
My second tier would be:
Exosquad
Better Off Ted
Running Wilde
Stargate Atlantis (Shepard and McKay made such a fun duo)
Edit:
After reading over some others, how could I have forgotten Terminator: Sarah Connor Chronicles! Oh man, that shows got so good in the second season...