Arduino is a great starting point for electronics, and with a motor shield it can also be a nice tidy platform for robotics and mechatronics. Here is a design for a full-featured motor shield that will be able to power many simple to medium-complexity projects. Build the kit, and learn how to use it with these detailed instructions.
Once soldered together, the cable plugs between the Pi computer and the Cobbler breakout. The Cobbler can plug into any solderless breadboard (or even a prototyping board like the PermaProto). The Cobbler PCB has all the pins labeled nicely so you can go forth and build circuits without keeping a pin-out printout at your desk. We think this will make it more fun to expand the Pi and build custom circuitry with it.
This TFT display is big (2.8" diagonal) bright (4 white-LED backlight) and colorful (18-bit 262,000 different shades)! 240x320 pixels with individual pixel control. It has way more resolution than a black and white 128x64 display. As a bonus, this display has a resistive or capacitive touchscreen attached to it already, so you can detect finger presses anywhere on the screen.