Task Specific vs. Platform controllers
Two directions are possible - task-specific controllers, often portable (pads, minikeys for iPad or laptop usage) and more platform-oriented master controllers that provide an integrated workflow for DAW systems, offerings keys, pads, faders, transport controls, step sequencers, and more.
Ableton Push and Native Instruments Maschine are probably the best known examples of a pure proprietary platform approach that goes deep by combining hardware and software functionality in a unified platform, offering real focus. The goal is to build a workflow that keeps you hands-on with the controller while using the computer. It takes a good bit of science to use a Push or Maschine controller with other vendors' hosts though. The approach overall has both advantages (incredibly tight integration) and disadvantages (try using a Push with Logic or Digital Performer).
I've been very impressed with my Nektar Panaroma 4 for its lovely execution in supporting a variety of DAWs with very detailed hands-off workflow that pushes the envelope with dedicated support for DAWS as well as dedicated support for specific instruments and plugins within the DAW environment. For one, the controller keeps growing in useful value, as the Nektar team rolls out more integrations with software - starting first with amazing Reason integration, adding Cubase 7 support last year, and this year announcing support for Logic Pro X and, coming soon, dedicated support for Bitwig.
Nektar talks about how they've decided that the best way to support multiple plug-ins and multiple DAWS is to make sure that each tool gets a workflow that is optimized individually. This takes real dedication and not inconsiderable software development, but the results seem even more impressive under your hands than this video fully conveys. (In fairness, it's got a learning curve, but a learning curve that's got the same kind of payoff as learning the key commands in your favorite software.)
(For more details on Bitwig itself, go here.)
Keith McMillen crowd-funded his first controllers, and this year's update walks all over their original SoftStep floor controller, changing the foot button layout based on customer feedback with their newSoftStep 2. I like how this company gets its cues from its userbase and yet still manages to provide affordable, innovative control surfaces.
This is one video that synthesists cannot miss