Pulling my partial list from a previous thread:
Life on Mars (UK), Veronica Mars (came to mind because of LoM, but a great series and I :heart: Kristen Bell), The Wire, Lost, Traveler, The Lost Room, Supernatural, Firefly, BSG (seasons 1 and 2 were best, not so much later), Arrested Development, Prison Break (season 1), Twin Peaks, The Unit, The Dead Zone, Buffy/Angel, Rescue Me, Doctor Who (the resurrected 2005-2009 series), Dark Angel, John Doe, Alias, The Pretender, Stargate SG-1 and Atlantis, Community (only first episode aired so far), The O.C., Roswell, Futurama, Spaced, Torchwood (more the mini series, "Children of Earth" than the regular series), Dexter, Sliders (last 2 seasons aren't as good, last season sucks compared to first 2), Burn Notice, Quantum Leap, Journeyman, Tru Calling, Dollhouse, Dead Like Me, Jericho, Smallville (really mixed feelings, haven't watched past season), One Tree Hill (haven't seen past season 3), Babylon 5 (I never finished), Farscape (saw most of it), Sleeper Cell, 24 (saw first 6 seasons), Warehouse 13, Life, Castle,
This is assuming you don't like anime, there are at least 15 anime series I would recommend (though I'm not up-to-date on anime from past 2 years or anime prior to 1995 aside from a few series).