One of my raspis is intended to be an electronics experiment, using the logic from the pi to manipulate TTL.  Towards that end I am looking for some tools that help that kind of experimentation, and I've found these things :

Cover with Breadboard Area for Raspberry Pi - Large

Once you have that together, you'll need a breakout cable for the raspi - like this :

How to make a breakout adapter (instructibles.com)

Or alternately you can buy one from adafruit.com :

Adafruit Pi Cobbler Breakout Kit for Raspberry Pi 

To wrap it all up - let me present to you a simple project put together by the good folks at liminastudio.com.

Tutorial: How to use your Raspberry Pi like an Arduino

Until next time kids, happy hacking and remember - you don't stop playing because you get old, you get old because you stop playing.