The Si5351A clock generator breakout from Adafruit allows you to generate any clock frequency from 8Khz up to 160MHz. The clock generator is an I2C controlled. It uses the onboard precision clock to drive multiple PLL's and clock dividers using I2C instructions. By setting up the PLL and dividers you can create precise and arbitrary frequencies. There are three independent outputs, and each one can have a different frequency. Outputs are 3Vpp, either through a breadboard-friendly header or, for RF work, an optional SMA connector.
In addition, the board has a 3.3V regulator (LDO) so that it can be powered from 3-5VDC. There's also level shifting circuitry on the I2C lines so you can use this chip safely with 3V or 5V logic.