There are many places on the web where you can legally watch TV and movies. There are also some more questionable ways to watch TV and movies however we aren't going to go into that today. The different ways that you can watch stuff online are as follows, Website (Flash), Website (plugin), or program (bittorrent or streaming client). A couple examples of Flash websites that have plenty of content are Hulu.com and Joost.com. I have use both of these extensively and they offer good quality TV and movies for free.
If you are a Netflix subscriber you also have access to view many movies and TV shows instantly. This does however require a plugin. If you are a firefox person you will have to run this through ietab, however as we speack I am watching the original episodes of Hitchhikers Guide to the Galaxy full screened on my second monitor. "Don't Panic" Netflix has done a great job of ensuring qulity, and smoothness.
If you would like to watch TV and Movies else where you can Check out Hulu.com and Joost.com both of witch offer a wide selection of TV shows and Movies. If you make a account with them (which is free) you can save things to a queue and be notified when there are new shows etc. This is a nice option for TV on the web because there are ussually options for hi quality and low quality, and you can pause any of these videos and watch them at your leisure. For people sponsored tv you can also turn to Democracynow.org.
Last of all are the programs. There are a few programs that will let you watch video streams, Winamp , TVUplayer , Miro, and Vuze. The first two do exactly that they play streams of video, and the pause feature is extrememly limited and ill advised. However the last two Vuze and Miro, are quite different. Vuze is a bit torrent client that recently has started making it easy for poople to release their video and other creations. You can choose to download them or play them. Miro on the other hand is still a video client, however it downloads videos or podcasts that you subscribe to (for free) and allows you yet again to play them when ever you choose. Unlike the other options for watching TV and Movies these last two can use up alot of space, however with space being so affordable nowdays, that really shouldn't really be a big concern. If you have questions or would like me to look over a program that you use, let me know by leaving a comment or contacting me.