[Al Skierkiewicz]

Ryan,
You can use piezo buzzers in place of speakers. They are easy to interface and can play out a band of frequencies. At least one of the Radio Shack devices is listed as midband 1500-3000Hz. That is certainly enough to give you R2D2 like sounds. They are very efficient giving upwards of 90dB+ outputs at 10-15 ma. Most can be used as the collector load in a simple one transistor amp. Since the current demands are low, a 2N2222 or 2N3906 would work fine. When you choose, be sure to look for one that does not self resonate, i.e. make sound when connected to a power source. Most are able to take a variable frequency input.