Here is a very wee motor control board for your Pi from the UK, PiBorg:

With PicoBorg, you can turn on and off fans, motors, solenoids, relays etc. from your Raspberry Pi.

There are 4 low side drivers so you can turn on and off 4 devices
One is connected to the RPi PWM pin, so you can vary duty cycle (normally vary speed).

Only £5.99 or Available with cables for £9.99

Example uses

• 4 fans on/off control over all and vary speed on one fan
• 4 solenoids
• 4 DC motors (on / off control over all and vary speed on one motor)
• or a combination of these
• or control one 6 wire stepper motor in both directions

Read more.

Each Friday is PiDay here at Adafruit, be sure to check out our posts, tutorials and new Raspberry Pi related products. Have you tried the new “Adafruit Raspberry Pi Educational Linux Distro” ? It’s our tweaked distribution for teaching electronics using the Raspberry Pi. But wait, there’s more! Try our new Raspberry Pi WebIDE! The easiest way to learn programming on a Raspberry Pi.

We now have Raspberry Pi Model B with 512MB RAM in stock and shipping now!