GO HERE to watch all Star Trek episodes online. This is a great archive and points to video sources all over the net. They include ST Original series, as well as Next Gen and all the spinoffs! WARNING: Not all of this is hosted in one place. This means that depending on the episode, it’ll come from different sources. Some of these sources are malware sources, so be really careful!
[thanks Michael]
Inane World 
FYI, as of 5/6/11 that sites account has been suspended…just checked it….bummer 😦
quite right – looks like they haven't paid their bill this month – LOL
I guess we'll have to see if it comes back up or not.