Xbox Live Arcade
Geometry Wars
Heavy Weapon
Street Fighter II Hyper Fighting
Hexic HD
Smash TV
Texas Hold 'Em
UNO
Assault Heroes (Just Free Trial)
Galaga (Just Free Trial)
Novadrome (Just Free Trial)
Small Arms (Just Free Trial)

I got Uno free from a friend, Hexic came with the system, and Texas Hold 'Em was free as well. The rest were worth the purchases, except maybe Street Fighter. Probably shouldn't have bought that one.

As for demos, right now I have Just Cause, Ninety-Nine Nights, Sonic, and Crackdown still saved on my console. I've had a lot more in the past, of course, but demos aren't really worth talking about anyway.

I don't think I would buy many Wii VC games unless they had updated resolutions to support widescreen or just nicer TVs in general, or had some added online multiplayer. Considering how easy it is to get access to a 10 year old game like Mario Kart 64, the only reason I'd ever purchase it again is for the ability to play it online. That's what these download services should be focusing on, in my opinion.