Ordered a Gertboard from http://www.tandyonline.co.uk which arrived 2 days later, even with the 3-4 day shipping option.
The Gertboard is a Raspberry Pi expansion board, which offers 12 buffered IO ports with LEDs, 3 pushbuttons, a DAC, an ADC, a motor controller, 6 open collector channels and probably the coolest of all, an Arduino microcontroller (Atmega328P) which can be programmed by the pi, using the standard Arduino IDE with tweaks from here. Here's a shot of the Gertboard running the 'blink' Arduino example sketch:
The Gertboard comes unassembled, and takes a few hours to put together. Tandy's packaging is excellent, with components in an ordered strip. There are a bunch of sample C programs to test each of the subsystems, which I'm enjoying working through to validate the soldering.