I've been listening to his Quantum Memory Power audiobook. It covers a huge range of memory techniques: memory palaces/journey method, mnemonics, visualization of numbers, etc. Some of his pop-culture references are a bit dated, but otherwise I find it to be a great system.
Funny you mention that, I listened to those audio CDs as well! I think that and "How to Develop a Perfect Memory" are the best resources on him, he's the man.
