dc42:
If your motor take less than 1A you can use this http://www.farnell.com/datasheets/39120.pdf. It comes in an SO-8 package, so you will need an SMD adapter board to use it unless you are designing your own PCB.There are some low-cost H-bridges around based on the L293D and L298N bipolar H-bridge chips, but they have a voltage drop of around 2V. So you would need a power supply providing around 8V for your 6V motor if you use one of those.
Another solution is to use a single mosfet to control the motor on/off and speed, and a DPDT relay to reverse it.
sorry, in my home there is no ic h-bridges i think.. even 555 is not available