I have chosen to feature Arturia's 61-key keyboard here, but they also have a 49 and 25 key version. Arturia calls these "Hybrid Synthesizers" because . . . well . . . they are. The keyboard itself is a sophisticated controller. The 61 features two sets of ADSR sliders, plus knobs for various parameter controls such as cutoff, resonance, LFO, etc. There are separate control wheels for Pitch and Modulation, plus 16 touch-sensitive pads for triggers and performing.
The software that comes with it has over 5,000 presets that model most of the classic synthesisers. It also allows you to tweak each preset to your heart's delight, and mix and match different synths/settings.
I truly love the touch on mine. Much better than most other keyboards. Of course, because it is a MIDI device, it will work with all of your midi compatible software as well. I use mine with Logic, Reason, and Ableton.
If you want to check out mine, contact me at: firstname.lastname@example.org