I got some Atmega8 MLF's and some Atmega128 MLF's in last Friday. The Atmega8's are really small in the MLF package format. Basically, it sort of looks like the old PLCC packages, except the little pads are about .020" wide and about .015" apart. Plus they have a center square pad that serves as a solderdown and holddown point. The pads are also arranged around the bottom edge or lip of the chip case, and don't extend up the side. The pads are also plated with a gold like substance and not tinned with solder like you would typically expect.
Now all I have to do is come up with a PCB that has the Atmega8 and two 3v motor hbridges on one PCB that is less than 1 inch square, and still have a place to put in a IR object detector or two and a line detector as well. What would be really neat is to get a small LM2621 or MAX1621 DC- DC 1.2v tp 3.3 ot 5v step up converter to work on that same size as well. The MAX DC-DC converter can handle up to 1 amp max, so I could run the two tiny swiss gear motors off the converter via the motor controllers too maybe.
I am thinking about whether backing up is really important or not. The nano-sumo bot can go forward and turn easily enough, one or the other motor off. Or maybe only use one hbridge for reversing one motor and run the other forward only. In this case, if the robot detects a line, it can do a reverse turn to the left and turnaround to the right and continue on it's way. Forward only saves a lot of space, only one small SMD transistor per motor, the other nethod uses one transistor and one hbridge.