Maxim DS1307 Mixed-signal and digital signal processing ICs | Analog Devices is an 8pin DIP RTC that uses a tiny standard clock crystal. If you do a search on the forums and also in the playground there are code and examples on how to use it. You can order samples from maxim for nothing and I got my crystals from toys in cornflakes boxes(no joke!) and old motherboards. Just look on any toy or old motherboard for a small round metal can that looks similar to an electrolytic capacitor, thats usually the crystal.