Check here to get your Wii setup for homebrew and here for what homebrew is available. The system is also know for its homebrew scene, almost rivaling the Xbox in that department. Even if you find it very cheap, don't buy it unless you're a hardcore Wii collector. It has no SD slot, no Gamecube compatibility, no internet connectivity, a top-loading disc drive, much worse build quality and composite video only. There was also the smaller, black and red Wii Mini.
They still can be used for Backwards Compatibility with homebrew loaders and classic controllers. Nintendo later stripped out the Controller and Memory Card ports with a redesigned Wii, and started using a new disc drive that couldn't read Gamecube discs. So check out its page if you're wanting more games than what's here.
Since it was essentially a GameCube on Steroids, it has full backwards compatibility with its Software, Memory Cards, and Controllers. As a result, there's a shitload of shovelware on the system. Tech-wise, it essentially is "two GameCubes duct-taped together" thus, it was pretty cheap and easy to develop for. How? Motion controls made for an interesting new gimmick and clever marketing aimed at the "casual gamer" people. Everyone though it would fail and that Nintendo would bow out of the Home Console race, but it actually became the highest selling system of the generation and Nintendo's highest selling system ever.