Weddingbee boards

I have this mat from jade yoga. It is all natural rubber very ice a thick. I teach a class called Bodyflow, a mix of yoga, tai chi, and Pilates. I have had my mat for over a year and it is still in amazing condition. It will smell like rubber when you first get it, butithe smell goes away fast. I got the extra long one. I'm 5'8 and like fitting my entire body on my mat during things like pigeon pose. 

http://www.jadeyoga.com/store/harmony-professional-yoga-exercise-mat.html

I am chiming in, very late to the party.  In my experience, what type of yoga mat you have doesn't really matter - all wear out eventually, ALL slip if your hands or feet get super sweaty, and all smell after a while.  What matters is what you put ON TOP of your mat.

I highly recommend investing in one of these - http://www.amazon.com/Yogitoes-Skidless-Premium-Size-Towel/dp/B000SQDI3C/ref=sr_1_1?ie=UTF8&qid=1328913000&sr=8-1.  You will never slip, it protects your mat from sweat, bacteria, and dirt, and you just throw it in the wash every few classes.  The best part, however, is that I can use it on top of my gym's loaner mat without getting squeeved out... makes it really nice not to have to carry my mat with me everywhere.