Hi Piglet,
I just read this message after posting in the Art Riggs thread. Sorry for repeating myself but I can highly recommend the Art Riggs DVD/video set if you're looking to expand into some advanced bodywork techniques, and his accompanying book is also very well written. It's not the cheapest set out there, but definitely worth the investment as there is such a wealth of knowledge contained within them and you'll return to them again and again.
Several people above have already recommended The Trail Guide to the Body, and I'd second all of the comments made - it's one of the best books I've ever used for advancing my palpation skills and getting a really sound understanding of what goes where, and what does what! It's worth the time and effort to follow the "lesson plans" the author lays out, but for the sheer brilliance of the illustrations alone I'd recommend this title to any bodywork practitioner.
Incidentally, the company who produce this manual have also recently brought out a range of other products to complement the book - including a DVD and student handbook with quizzes to test your learning. I don't think Ultimate Massage Solutions stock the full range, but the chap who runs UMS is a great guy and may be able to help. The Ultimate Massage Solutions workshops also look really good, he often gets highly respected practitioners from all over the world - I just wish he'd come to London more often as there are a few I really want to attend!
Andy
Edited to make more sense