When I did it back in 1999, we raised angel money right after we had a team & a short business plan with a powerpoint but not even an alpha product yet. Our idea required enough development work that we couldn't really manage while keeping our full time jobs. (http://web.archive.org/web/20001019030551/http://emfocus.com...)

And from what I've seen of the relatively new seed investment firms, you can approach some just as early - an idea, a team, and a plan (sometimes as short as a few pages). Some would prefer that you not even incorporate yet.

It was 1999, though, and likely less formal relative to the more mature market now. Back then it seemed most angels were friends or family of the founders. The boom was so strong that getting early investors was no more difficult than talking to friends who liked to invest. You could also work with an incubator but we didn't call those guys "angels."