On www.nuxie1.com i found a well designed function generator based on chip XR2206. This chip is a monolithic function generator integrated circuit capable of producing high quality sine, square, triangle, ramp, and pulse waveforms of high-stability and accuracy. The project’s page provide full schematics and pcb boards designed with Eagle. View details on the source site.
1MHz Function Generator based on XR2206 -[Link]