Multi-platform owner. Owned a Wii for about 6 1/2 months. Going to include rentals on the list since I've been renting a good bit more than buying since the beginning of this year.
First-Party (3): Wii Sports, Wii Fit Plus, Wii Sports Resort
Third-Party (13 retail plus 1 Wiiware): EA Sports Active (EA), Just Dance 2 (Ubisoft), Broken Sword (Ubisoft), No More Heroes 1 & 2 (Ubisoft/Marvelous), Muramasa (Ignition/Marvelous), Final Fantasy Fables: Chocobo's Dungeon (Square-Enix), Dragon Quest Swords (Square-Enix), The Conduit (Sega), Madworld (Sega), Resident Evil: The Umbrella Chronicles (Capcom), Harvey Birdman (Capcom), Ace Attorney: Justice for All WIIWARE (Capcom), Sam & Max Season One (The Adventure Company)
Third Party Percentage: 81.25% (82.35% if you include Wiiware).
I probably have the record here for smallest first-party share. lol. The Wii is my first Nintendo home console since the NES and of the SNES games I played on emulator, they were mostly jrpgs. So I never really got into Nintendo's first-party that much (a little bit on GBA and DS but very little of it on the home console side yet). I do plan to. The Mario games for sure. I liked NSMB on DS. The Wii's third party is pretty solid. But it gets passed over by the teenaged/adult male demographic for social reasons. A) The perception that Nintendo is "kiddie" and/or B) Their peers are on XBL and PSN, not Nintendo WFC.
If I were to look at ownership only, it would be 2 (Wii Sports and Wii Fit Plus) vs. 2 (EA Sports Active and that Ace Attorney WW). 50% Ratio. Or 2 to 1 in favor of Nintendo if you don't include Wiiware. So 33% Third-Party ratio. But since I rent like 6 retail Wii games for every retail Wii game I buy (4 to 1 if you count Wii Sports. lol), my collection isn't a fair representation of the games I'm playing.