A popular modding website that has only recently started offering high-quality Wii game downloads is Modio. I've been looking through some of their Wii download options to see if there are any worthwhile games that I can download and play on the Wii. The downloads include many classic Nintendo Wii games but also have games from different genres and eras. My testing didn't turn up too many games I would recommend downloading (again with the exception of Super Mario Galaxy and Zelda Twilight Princess) but it was a fun browsing experience and there were enough games that I found interesting that I thought I'll list them here for your enjoyment.
A couple of things I like about modio are its file managers and its console storage device compatibility. If you're familiar with the way Modio handles game discs and saves them to your computer, then you know how simple and efficient this system is. With just a USB flash drive or a USB pen (which you can get for relatively cheap at your local office supply store), you can upload your original Wii disc, select Wii modding files you want to backup and save it to your computer in just a few minutes. Using a CD/DVD burner program isn't required, but it does speed things up quite a bit and makes uploading/downloading Wii games much easier.
Modio also offers more traditional methods for backing up your original game disc and downloading games as well as using Xbox Live. It looks a bit complicated at first, but the programs it uses for these tasks are very straight forward and intuitive. From my testing, modio seems to be a very stable gaming platform, especially considering it's new storage device compatibility. I haven't had any problems with lag or bad performances yet, but if you're going to be playing at home or at work or anywhere else, then you may want to consider backing up your Wii disc and other Wii games using the methods Modio provides. It's definitely worth looking into.