Amy S

youtube, lol i just search for the name of the episode/show and "part 1" or "pt 1", because that way you often weed out random clips from the show.

also, i second sidereel.com; excellent site.

if you can find them and are willing to download the software, veoh(.com?) has a lot of full-length stuff.

also, watchtvsitcoms.com is excellent, but their selection is more limited.

last and probably least, try the network's website. often they'll have a few random episodes or even all the episodes from the most recent season. this is hit or miss, though, and they intersperse the eps with commercials that are quite annoying.

hope i could help!