New Arduino library for the DS3232 real-time clock IC
If you're not a fan of using raw I2C-commands with a real-time clock IC, check out the new Arduino library for the DS3232 by Vino Rodrigues. Unlike other versions, Vino's library uses the official Arduino time library, and thus more portable. You can easily set and retrieve the time and date as well as read the onboard thermometer, set the alarms and choose whether the alarm interrupt or square-wave generator is enabled. It's a great addition for a very useful component.
When making your own clock - don't skimp on timing accuracy - so consider using our real-time clock module based on the DS3232 - with a temperature-controlled oscillator it is highly accurate, and has an onboard backup battery for when the power dies and 236 bytes of non-volatile memory for user data.