MyP2P is the best place I have found to watch sport online. It doesn't host any of the video's itself, but is more of an index. I was first told about it by a friend when I didn't have SKY Sports and had to listen to the football (soccer) on the radio. But the site carries more sports than just that. I still use the site regularly to watch my favourite teams from around the world play in different sports, and I use it a lot if say, I'm in the USA and desperately want to watch the Champions League match but can't find anywhere with the Fox Soccer Channel.
The site is easy to navigate and I recommend changing the time zone to match yours. The streams may not be listed until perhaps an hour before kick off in order to stop the powers that be from taking them down. For a big champions league match, you can see about 50 different streams whereas watching a lowly SPL game, you may only see one or two. Many of the streams require programs to run them, such as Sopcast or a plugin for Veetle TV, but many are just links to sites like justin.tv. Generally the higher the bitrate the higher the quality.
If anyone has any other good sites for watching sports online, let me know!