Check the FAQ for some of the things that come up frequently, and also visit the recruiting page for all the info you need on signing up and the application process!
Visit the Costume Reference Library for information on currently recognized 501st costumes. This library is pretty extensive, so make sure you have some time on your hands! Also of interest is our Guide to CRL's and New to the Legion Costumes.
Review our Legion Charter, Operating Protocols, and Council Resolutions. Reading our Mission Statement is pretty useful, too. These are required reading if you want to become a member.
The Trooper Survival Guide is a great reference for both existing 501st members and those thinking of joining. It contains information about what to expect at events, the history of the club, and much more!