Here's the "H bridge" with only 2 transistors:
That's not an "h-bridge" - its more like a "half h-bridge" (half-bridge?) like I was describing (note the dual-ended power-supply). Its advantage is in the fewer number of parts required. Its disadvantage is in the need for a dual-ended power supply, which can lead to issues of its own - especially if doing a battery powered design. This was a problem with the Milton Bradley Big Trak - since most of the time, the motors were being driven in the forward direction, you would end up with one half of the battery bank having a lower voltage than the other half, leading to issues of the other half trying to back-charge the lower half, causing you to have to change the batteries constantly in that toy!
;D