If you have a problem with invasive plant propagules clinging onto your clothing, you may want to check out BurzOff, a tool designed specifically to remove burrs, beggarticks, and other spiny seeds and fruits. It's made from 90% post-consumer recycled materials, and looks kind of like a pumice stone.
Actually, all the burry, spiny things I can think of that cling to my boots and jeans here in Massachusetts are native. But if you're in a part of the world where you're dealing with lots of thistles and grasses, you may find this useful (could have used this for the legumes in the Costa Rican pastures!). If you are already sold, you can get one for $8 + $4 S/H. Read the original press release here.