[Al Skierkiewicz]

I suggested the LM386 since it is designed for low impedance loads. A speaker connected across one of the digital outputs will likely exceed the current rating on the driver trying to sink current with an 8 ohm load. A 1mmf/16v electrolytic cap in series with the input should handle most frequencies you send it. The chip is self biased for single polarity power and can operate down to 4 volts.
If you are using one of the piezo devices, a simple single transistor driver should work fine.