If you are looking for a kit that is strictly for fun, the DutchTronix Oscilloscope Clock Kit is a good one!

The clock kit drives an oscilloscope in XY mode. There are an amazing number of modes for the clock face and everything can be done by way of the single push button control on the board or an RS-232 interface to a computer can be used. The clock board runs on 5 volts and about .01 of an amp.

The kit is really quite simple. However, one word of warning; there is no step-by-step manual, you must know your way around a circuit board in order to get the diodes in right, the chips facing the right way and the electrolytic capacitor in the right polarity. Not ideal for a first timer but if you have done a few kits before this one is great entertainment and very inexpensive. http://www.dutchtronix.com