I'm using "DS-1307" for RTC (Real Time Clock). I've used I2C (Inter Integrated Circuit) protocol (aka the TWI-Two Wire Interface) to hook up this IC.
It can not only manage time with accuracy up-to 1 second, but it also manages complete calender with day, date,weeks passed,months and years. And it also caters for the leap year:)
"Here" is a link to the data sheet.
Another thing worth mentioning that this IC can maintain time and complete calender for up-to "10 Years" with a single Li-Ion (3Volts) backup cell.