Check your library. Disclaimer-- I'm a librarian, but this is a great resource.
I preview workout dvds by borrowing them from the library-- it has saved me tons of money (because I find most aren't worth owning!) And my library is always buying new ones each month as they are released so I know I'm getting the latest. I can also request specific titles and the media librarian will usually buy them for the collection.
Plus, I get to change up my workout a lot so I don't get bored!