What you want is probably a MIDI controller keyboard. Most MIDI keyboards use the USB Protocol, so no problem there with connections. Then it's usually just a case of assigning the I/O module in the DAW.
This the absolute minimum MIDI Controller keyboard.
One great function of most modern DAW is to actually learn different functions and assign them to keyboard controls, so most keyboards can actually have various effect and patch parameters assigned to various buttons and knobs on the keyboard. This is a bit more upmarket and considerably more than I use:
The good thing about button assignment is that it allows you to re-create layouts on the MIDI controller, as if it were a 'real' synth. So you can set the resonance filter to one knob and the waveform shape to another, envelope adjustments and even effects like reverb, compression, phase et al. Look into it. There's nothing complicated when you get into learning the basics.
I've never used Reason, but I've heard nothing but praise for it. I use Logic Express 7 (will be upgrading to Studio 8 eventually), which only has limited synth capacity built in, but is still enough to tinker with.