Anime Expo, which my SO and I loved last year, already has their 2006 registration available online. My SO and I just found this out today, and it turns out that tomorrow is the last day to get the cheapest 4-day tickets. If you register by March 15, a 4-day ticket is $45, the same price as a 2-day ticket purchased later in the year, and only $15 more than a one-day ticket. Based on our experience last year we definitely want to go for more than one day this year.
This year they're actually going to mail out badges ahead of time, so there (hopefully) won't be long waits in line to get the badges.
[Update: I guess it would help to include the dates and location: Anime Expo 2006 will be held July 1 to July 4, 2006 at the Anaheim Convention Center in Anaheim, CA.]