Real Time Clock
I've built several clocks now and I have had good results with the NJU6355 RTC. It is available from DigiKey as an 8-pin DIP for around C$2. The manufacturer part number is NJU6355ED# and the DigiKey part number is NJU6355ED#-ND.
The spec sheet is available from either DigiKey or the manufacturer link above. There is also an application note which I cannot find a link to anymore. A search turns up one hit to a page with a broken link. Anyway I placed a copy if it here. The application note contains information on the crystal requirements and explains the test mode I use to measure the oscillator frequency.The application note is a little vague on what capacitance crystal to use. The crystal is 32.768 KHz and is available in several load capacitances such as 6 or 12.5 pf. Crystals are cheap and readily available. Since the frequency changes with the layout of the circuit (among other factors), it is hard to be precise about the accuracy. But if you get the right crystal and lay it out properly, the accuracy of the RTC is amazing.
VE3LNY's Electronics Notebook Page