Open Source FPGAs using the MyStorm BlackIce II
This project is maintained by piersh
An FPGA can be used as a signal generator by using Direct Digital Synthesis.
The fpgafun site has an article on Direct Digital Synthesis. The examples can easily be converted to run on the BlackIce II.
Here is the first SimpleDDS example using an Alinx AN108 to generate a square wave at 1.39Mhz.