Novation makes some great controllers. I use M-Audio Oxygen 49 and it does everything I need for soft synths.

bitflipper

Check out the Jordan Rudess Omnisphere demo on this page to see a secondary mini keyboard in use as a keyswitcher. 

What a great idea! I had considered a smallish live setup using a combination of two controllers, like a 61 and a 49, to handle two-handed parts. I was thinking along the lines of more flexibility and two lighter pieces of gear as opposed to one 88-key monster. I hadn't considered that the left-hand / bass controller could be used for keyswitches. That's brilliant!
 
To the OP - I have a Novation ReMote 61SL in my studio. I got it thinking that I'd use all the knobs and faders for controlling all sorts of things in SONAR and on synths and FX. Like other posters here, I ended up just using the mouse, which I then upgraded to a Kensington trackball, which is very nice and easier on my joints. (I notice in the video that Jordan Rudess uses one - so maybe I *am* trying to be like him. ) Just my experience - but your preferences may be different.
 
That said, I am thinking that the extra controls will make more sense in a live setup, where the mappings are likely to be more fixed, for example, where you may have the faders control the synth levels in a stack, and knobs controlling EQ or overdrive in an FX chain.

I have m-audio axiom 61.. good build quality , not great to config

novation 25sl mk 2.. not great build quality considering the price, to a point where I won't buy one again due to that.. first one I had keys weren't even level !! .. so so with automap, but for custom setup in sonar.. bit of a mare again

m audio ozone - much like the oxygen .. only 25 keys , so so .. but I'm not a fan of how m-audio support is none listening when drivers don't work for 3 months!!

just got a korg microkey 61 the other day.. only coz I wantd korg legacy software.. drivers for it are a nightmare.. won't reinstall correctly on win7 64 bit . (can't use sustain pedal)

the price of keyboards has gone up I did notice from buying a few 

but if your SOLELY using sonar exclusively I bet the roland / cakewalk keyboards are the most straight forward.

a sustain pedal is really nice, even if you don't go mad on playing . makes a big difference :)