Here's a little vehicle I picked up in a bundle from eBay. I really like this small 6-wheel machine, it reminds me a lot of the moon buggies from Space 1999. I painted this up as a construction/civilian vehicle rather than military and painting the yellow made a pleasant change from camo greens and browns. I'm now tempted to steal the kids toy diggers and build a set of mining/colonists.
You can get these from Ground Zero Games and they come in several options, armed or unarmed and with trailers etc.