You will notice that there are diodes placed across the mosfets. Usually mosfets have internal diodes, but it is a good idea to add external diodes, just to be safe. These diodes should be high speed schotky diodes, with an appropriate current rating. When motors rapidly change direction, the back EMF generated inside the motor can damage mosfets. These diodes are in place to absorb the back EMF, and to keep the mosfets safe. Do not ignore these diodes, as they are necessary to keep your H-Bridge from being destroyed.
When choosing mosfets, it is important that they will be able to handle the maximum current required by your motors. This is the stall current. If the mosfets you chose are insufficient, it can cause your motor driver to go up in smoke if your motors approach stall. I have used IR530 and IR 9530. Also note that all the transistors must be from the same company (this is not written in any book, its my own observation), otherwise you may have heating problem. The above model has been successfully implemented on the robot, report of which will be publishes ASAP. Thanks.