If you aren’t looking to build your own models or just looking to easily expand your collection, there are quite a few radio controlled vehicles available off the shelf. The Siku Control 32 series is very good and I highly recommend the Orlandoo kits which allow you to assemble your own top quality 4WD RC jeeps.
Hover the mouse pointer over an item and arrows will appear allowing you to scroll through the different items in a category. If you hover over the picture you can get a slightly zoomed view.
Siku Control 32 Models
The Siku Control 32 range are the best off the shelf RC tractors you can get.