I got an L298 with the switches for my preliminary project. I got it working tonight. The L298 is a fairly powerful motor controller--with two 2 amp channels, most robots won't need more. The two channels can be paralelled for 4 amps, and the voltage can go up to 40 volts or so. I'm not sure l298s will work for the big tank, but for the drive on the 1/16 plastic model, it'll be fine.

http://www.pyroelectro.com/tutorials/l298_control/index.html
This is the best I found in a few minutes of google to find a tutorial. Keep in mind that the L298 comes in two versions right now--an older L298N, and a newer L298NH. On the data sheet for the N, it points out a need for filter diodes on the motor feeds. The NH has these built in. Thus it will be much simpler to wire. Keep in mind that larger motors than the 6V Erector set motor I used will probably need a heat sink on the motor driver to help keep it cool.

I got the driver from http://www.taydaelectronics.com one of many electronics outlets on the web. They had the microswitches I needed for a different project for much less than others, and since they wanted a $5 minimum order, I grabbed the L298 at the same time, knowing I'll need it for the tank eventually. Electronics are like everything else, you sometimes have to shop around. A big thing about Tayda though is that they're in Thailand. If you order something, keep an eye on the shipping options, the standard will take anywhere from one to three weeks to arrive. They also have higher prices on other components--the dozens of LEDs and resistors I needed for my other project were better gotten from Mouser Electronics.