i can vouch for the AD9850 modules, if you want something more permanent, and arduino is your tool of choice, get a uno, a breadboard shield and a lcd shield, download the bog standard code, run out an encoder or keypad off the breadboard shield and boom variable frequency source, then add some op amps to level shift and amplify and you have sine and square covered,
i went a little further with one of these writing various patterns more relevant to my job,