I bought one of these last year:

http://www.ebay.com/itm/262326560037

The advantage of this module over the bare oscillators on the page you reference is that it is ready to go, complete with dual outputs and power input, and has been calibrated -- no NIST certificate or anything, but from the photos and description, he seems to know what he is doing. From what I can tell with my limited test capability, it is accurate and very stable. If you have better equipment, there is an adjustment on the board.

However, it is a sine wave output. As a reference, a nice sharp square wave might be easier to use.