Gaiam Grippy Yoga towel with non-slip backing:
It is double sided: one side with a towel like material and the other you put face down on the mat that is non-slip (has a plastic backside).
I really like this towel. It stays on my mat better than the Jogi Hot Yoga Towel I have tried, which also has a non-slip backing.
It is a fairly thick towel and comes in two colors: purple and green.

I bought this towel at the Real Canadian Superstore for $39.99CAD. Although its a little pricier, it is still cheaper than towels from Lululemon, etc.

I've used this towel in my 30 Day Moksha challenge, for Moksha flow classes (intermediate flow class). I found that it doesn't move around when I pivot my feet around or adjust my stances. This is probably because it is so thick compared to other towels. It spans the entire length of my mat (standard yoga mat) and it lays flat.

It absorbs sweat and dries fairly quickly after class despite its thickness. However, when you wash it, I found that it takes a while to dry. It says to dry flat but I don't have space to do that. Instead, I hang it across 2 hangers and have to flip it around to make sure both sides are dry. The towel side also seems to pick up a lot of lint.

Rolling this towel makes it fairly bulky to put in your yoga bag. It could even rival the size of some yoga mats I think hehe.

Overall, I do think this is the best towel I've tried so far (that's available in big superstores). I really like it and might even buy it in green!