I popped into this thread expecting mentions of music videos. Normally I'd leave satisfied-- YouTube
is the new MTV-- but there are other things you can watch too. If you're into standup comedy, there are classic bits from just about everybody-- Bill Cosby, Jerry Seinfeld, Eddie Murphy, George Carlin, Jeff Dunham (his Achmed bit is one of YT's most watched ever), John "You Go NOW" Pinette, and lots of good yet more obscure ones too like Jen Kober.
YouTube is also the ADHD teen/post-puberty TV place, with stuff from Fred (trust me, he's easier to stomach in his original three-minute vignettes than the movie), Shane Dawson (definitely NSFW) and The Annoying Orange (kid-safe) among others.
One great viral video aggregator guy is Ray William Johnson; he review three viral videos every episode, with funny commentary.
Best of all,
YouTube +
tv = No Annoying Pop-Up Ads Or Annotations, FTFreakin'W.
EDIT: But wait, there's more-- WAY more. It's like Rule 34 (?) of the Internet, for video. Special XBox gaming tips and tricks from the Achievement Hunters, to old-school analog synth demos from Retrosound.de, to drag queen makeup tips from Blanche Babcock-- just about everything except hardcore porn.