You can view information about the Ask Hall of Fame here: http://www.askhalloffame.com/. The Hall of Fame is not something you can join, but rather you get selected to be in the Hall of Fame based on your great contributions to the community.
I was inducted into the March, 2012 Hall of Fame. Its a way to honor some of the Ask.com users who demonstrate a positive example by answering questions in detail with the best possible accuracy, as well as ask good questions that can be answered accuratly. They also demonstrate good grammar, spelling, and give off a positive vibe. -S-