I'll have to say Truggy. No specific brand or anything, they're just the most capable for the money... although I'm sure you'll get a lot of specific recommendations. They're also very popular for racing, unline the "Monster Trucks" which have limited popularity in actual racing.
Specific brands? Well, you can see from my signature what I personally prefer, but you can't go wrong with any of the "major" brands. It is a good idea to see what brands your local hobby shop carries parts for- nothing worse than wanting to go play but your truck is broken and you have to wait for a part to be shipped.
Xray, Mugen, Losi, Kyosho (pricey!) Associated, Jammin are ALL great trucks. If you are really on a tight budget CEN or Thunder Tiger aren't bad, but be sure you can get parts.