For the past couple of weeks I have been working with the DS3231 Maxim. This chip is a I2C based RTC with an integrated temperature compensated oscillator and crystal.This means despite changing temperature conditions, it will maintain a very accurate track of time. If you’re interested in the first rev of the PCB, let me know. I have a few available. They are functional, however, the prototyping area came bad.I have a set of new ones with a proper prototyping area, reset button, and power LED in process.
Check out more on the Accurate RTC Shield Project Page