If you're interested in watching TV right away, I recommend you try MyTVPal.
MyTVPal has a wide selection of shows, some of which might even be worth watching. Categories include Animated Shorts, the ever fascinating Archeological Channel, Music Videos, Internet radio, and a long list of stations from Argentina, Aruba, Australia, and, well, I got tired of scrolling down the list. From the pull-down menu, I switched to a list of 80 channels in the United States (with plenty of opportunity to see ads because there are just 10 stations per screen). Many were local channels -- community-based city council meetings for instance, as well as plenty of shopping stations, just like those you probably ignore on cable. One possible bright note was a Webcast from an NBC affiliate in Anchorage, Alaska -- until I discovered it was from December 3, 2006.

MyTVPal's list of channels in the States
I thought movies would be fun, but they weren't because choosing a movie is a guessing game. The description is valueless: "Ch. 14008 Feature Film Channel 8." I Iooked for Spiderman 3 (ha!), but among the titles I did find on the movie channels were "The Big Bluff," a 1955 drama, a Mack Sennett short, and "Beyond Bengal," a 1934 jungle exploitation flick that the IMDB database calls "The record of an expedition deep into the Malayan jungle." Whoa.
MyTVPal's viewer is mercifully easy to install and use, though unlike Joost (which I'll talk about tomorrow), the menu isn't transparent, so I can't watch anything while strolling through the listings.
Tomorrow: Joost and a handful of other Internet TV sites.
Quick Note: In yesterday's blog, in Comments, two readers mentioned Internet TV sites worth a visit: MediaHopper and FindInternetTV. They're both worth a look. [Thanks Brant and SunTzu!]