You leave out a ton of important information from your question. Namely, do you have a set number of competitors? Is this a seasonal system or is it a one-time deal? Etc.
If this is a tournament (i.e. a one-time deal with a known number of competitors), round robin is theoretically the fairest way to run it. After the round-robin phase, you move into the single or, preferably, double elimination phase.
Now, since you mention Battle.net, you need to realize that Blizzard uses the Elo system for stuff like WoW arenas (and a similar algorithm for Battle.net SC2 seasonal rankings). Elo is pretty simple, and Wikipedia gives a great overview of how it works.
A simpler (and Microsoft thinks better) algorithm is TrueSkill. Read (a lot) more about it in Jeff Moser's blog by clicking here. The math may look scary, but it's really not that interesting.
I'm not really sure what you mean by "voted wild card system", so I'm afraid I can't address that part of your question, but both Elo and TrueSkill (and to a lesser extent round robin) should meet most, if not all, of your requirements.