I want to make it dirt simple for users coming to my site to register so they can post comments, vote on things, etc. I would like for them to be able to use their facebook id, twitter id, yahoo mail id, gmail id, AIM id, msn id, or whatever else people are likely to have (not necessarily all of those, but the more the better). I want my mom to be able to do it in 30 seconds or less. (that is, no "enter your open id url here" type thing that would confuse her). I prefer they not have to pick a unique name, as that gets annoying as the site gets more users and it gets hard to find one that is unique.

What is the best option here? I'm not quite sure about OpenId vs. OAuth, and whether there are other options. And I'd like it to be as simple for me, the developer, as possible (of course!). I don't want to spend forever learning some protocol, nor have to structure my whole app around this. It would be great if there was a site with sample code that is pretty easy to drop in.

BTW, StackOverflow is a good example of a site that was easy for me to register for.