Gaiam does offer a few different rubber alternatives: but they don't have third party, or any party for that matter, informing us how the rubber is harvested, how "natural" it really is and the percentage of latex to bind the rubber together. They have an "earth lovers mat" that's made from recycled materials and natural rubber- although I'm not sure about the stickiness, and exactly what the recycled materials are- call me a skeptic. Plus it's kinda poo coloured... eww.
Jade on the other hand- offers ONLY natural rubber mats. The Yoga Loft sells them and I got a chance to touch one and smell it (twice!!). It did smell slightly like rubber (compared to the strong smell my Lotus Wear mat!). A few washes and air dried should help with the smell. They explain how the rubber is "tapped" from the rubber tree like maple syrup (this Canadian girl totally gets THAT reference!), the percentage of rubber vs latex, where the mats are made (USA-they resisted the China trend) and they give 25 different ways to reuse your old mat!
The Kicker: you buy a mat- they PLANT A TREE! Enough said. Oh- and they are affordable too, from 59.95$ up! YAY. :)