Well if you want to buy an online multiplayer game with Wii Points, you'll have to check out the WiiWare part of the Shop Channel. Alternatively, you can go here:
This is a list of all the WiiWare games available in North America, with links you can click to read about each one and whether or not it has multiplayer or if it's the kind of game you're into.
My only suggestion for a multiplayer WiiWare game to get would be Bomberman Blast, because it's the only one I have.
Hope this was helpful.