The iPhone has so many great music-creation apps that they deserve their own category, but shiny dedicated instruments like Korg's new 37-key sampler are always nice. It has a line-input, goose-neck microphone, and editing software for the Mac or PC.
Korg's nanoSeries line of noise makers are unlike other Korg synths because they rely on computer production software to work. The slim, USB (data+power) devices are made to be portable, so you can take your studio on the go. nanoKEY is a 25-note keyboard, nanoPad has 12 Akai-style sampler/drum pads and Kaoss pad, and…
PingMag did an interview with the creators of the Tenori-on that was overlooked when published, but there are a few interesting tidbits from the interview, like the fact that neither of the creators are musicians.
Hate having to bring an unnecessary amount of hardware when you want to produce your next musical opus on the go? Need more than a Boss 303 drum machine? The Trinity Audio Group may have what you're looking for with their linux-powered digital audio workstation.