Here's a nice one for Mac-using amateur musicians: Apogee's ONE is a multifunctional handheld device that features a built-in mic, preamp, and dedicated input/output. It works over USB and is designed for Garage Band, Final Cut and the like.
It's a single input, stereo output device, offering 24-bit audio between 44.1 and 48KHz sample rates in a package around the same size (though thicker) than an iPhone. Apogee's putting emphasis on the built-in mic (they even offer a stand so you can treat the whole thing like a handheld mic), though it's got one input for instruments or your own mic. That input is coupled with a preamp, customizable using the ONE's controls.
The ONE is designed to work with Apple's range of audio software, including iTunes, Garage Band, Logic, and Final Cut, though we don't imagine it would have trouble working with non-Apple software as well. It remains to be seen whether the built-in mic is everything Apogee claims; on such a small device, we're skeptical but remain hopeful. It'll be available sometime in "late July" at a pretty reasonable $250. [Apogee]