Cosmo's Factory has great images, info and assorted random crap.
The Rocky Horror Purity Test is fun for the whole family.
The Rocky Horror Picture Show in 30 seconds, reinacted by bunnies is hilarious.
Zenin's RHPS Archive has more images, info, etc. It also has a downloadable version of the RHPS video game.
The Anal Retentive Costume List has everything you could ever need to know about making costumes for Rocky Horror.