I want to do a double next year and I'm looking for suggestions and any personal experience you might have.

I've heard a ton of good stuff about STP, but it looks like STP and RAIN are on the same day in 2006, and there's no way I'm skipping RAIN (too much sentimental value for me).

Random points:

Location doesn't matter, hills are a good thing, registration shouldn't end more than a month before the event, I'm not too picky about the food at stops, June-August is best, but not set in stone.