When I was studying my underbelt katas I could always refer to Master Jhoon Rhee's books covering the kata. Those books are no substitute for learning how to perform the kata with my sensei, but provide a decent reference if I loose my place or get confused over the order of techniques.
Now, I'm learning my first black belt level kata: Bassai. The art I'm learning uses TKD katas for 10-1st kyu katas, but switches to pulling from another discipline for the dan katas. I've gone through the kata several times with Sensei, but still finding myself getting confused over the order of techniques from time to time. When I'm in class, I can always get corrected but outside of class I'm relying on faulty memory. I just want to make sure I'm reinforcing the proper form rather than incorrect form.