There are quite a few options for watching TV and video on the iPad, but one of my favorite TV applications doesn't actually play the shows. What's On? gives you the TV schedule with accurate channel numbers for any provider and location. You can mark shows as favorites and ask it to provide reminders.
Crackle is a free program that plays some old movies and 2nd rate TV snows. For free you can also get a PBS player, ABC Player, TMZ(an iphone app), and TV.com (CBS).
Another fabulous free program is Flixster. This program lets you find movie theatres by GPS and buy tickets online. It is integrated with Rotten Tomatoes for reviews. It also lets you set up a DVD list and supposedly interacts with iTunes videos, but I'm not sure how that works.
For less than $10 a month each, you can get Netflix and Hulu(the free version of Hulu does not provide the iPad app).
Lastly of course you have YouTube and any movies, TV shows etc. purchased off iTunes. Frequently websites will automatically pull up the YouTube app, getting around the no Flash issue, but sometimes you have search in YouTube for a video that was part of a web page.