Matt and Trey (the guys that make South Park) made this website where you can watch every episode of South Park free and uncensored. It contains short commercials, but it is definitely a good site.
This is a website that has partnered with NBC, FOX, and lots of other companies to bring you free streams of their popular shows. Some of my favorites are The Office, Scrubs, House, American Dad, It's Always Sunny in Philadelphia, King of the Hill and Futurama. They have tons of shows, you can check out the full directory of shows here. They also have a few good movies that you can check out here.
This website has a ton of content. It isn't quite as legal as the first two, but it has a lot more content. There are tons of movies (lots of which are still in theatres), and lots of TV shows. Some of my favorites are Prison Break, Weeds, The Sopranos, and The Boondocks. No ads, but sometimes the videos don't work.
This is the CW's site of videos. I don't watch this channel much, but I have some friends that really love it. The site looks pretty nice, and I'm pretty sure that the videos have ads in them.
I really only ever go to this site to watch clips of The Daily Show, but there are a lot of other clips from Comedy Central on there. It's worth a look.
This website searches for mp3s on private servers. It is technically legal since they don't host any of the music, they just link to it. It has links to both listen to and download a file.
A lot like the site above, but sometimes their download link doesn't work very well. The streaming is very fast and good quality though.
If all else fails just try BitTorrent!!! My favorite site for finding torrents is nowtorrents.com, it searches lots of different torrent sites and displays them in the same window.
Good luck! Post any sites that I missed in the comments (Seinfeld?).