nuelectronics.com, as I said before, have a neat little shield for data logging apps.
I've written a guide to accessing the real time clock on that....
The modest library from nuelcetonics takes care of many hassles associated with reading the RTC, and the shield carries the battery backup and crystal for the clock.
If you're using a clone, only 5 wires need be connected to the shield to access the RTC.
Cost of shield: GBP11, about US$16.
I hope the guide is useful to you, and saves you the "getting acquainted" work I had to do.
(If you DO find it useful, please click the Stumbleupon and/or Delicious links at the top of the page?)