Have a look at the M-Audio Axiom range, I've got the 49 key version and its a great bit of kit for the studio, semi weighted keys so they feel nice and solid, and some midi controllers etc, USB powered. Turnkey do them at good prices http://www.turnkey.co.uk
Defintaly the axiom 49. 25 is to small and the 61 is too big, i have onlt found one song which i needed 61 keys for and that is what you have transposing for The axiom gives you a lot more features than the oxygen, although the oxygen is better for reason. The Axiom is also great for non production, say digital djing using ableton live. Use the modulation wheel as the cross fader and the apds as all the different songs! Not great but it works well if u cant afford decks
that's exactly how i roll as well^^and im thinkin of getting the nanokey now. besides, there's octave buttons on the axiom25, so unless you're going to play chords n a melody w/ both hands, 25 keys is enough. just my opinion.