Korg nanoKEY 2 white

Pros:
Cheep and very portable, this is the sole reason why you should get it.
Mine had a code for some promotional lite versions of vst synths, reason limited and a 50$ discount coupon for ableton software, some may find those useful.

Cons:
Keys are a little mushy which some may find quite uncomfortable, you'd wish it had scissor switches or something.
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I suggest you set the velocity curve to hard, otherwise the velocity seems a little limited.

8-MONTHS-OF-USE-EDIT:
I'm afraid I can no longer recommend this product, it has a serious design flaw that would make me absolutely livid as it was the only thing I could use during my voyage.
You can push down on the keys topmost/bottommost and the whole key wont go down, only that side you pushed down, even leftmost/rightmost so some extent.
This may not seem like an issue, but it is.
To get consistent velocity you need to push on the keys dead centre, the above example simply shows the underlying cause. There's a reason all long keys on a computer keyboard have an additional hinge, it is to avoid this issue.
If the nanokey had vertical rails at the bottom and top points this issue wouldn't exist.
I guess I'll be physically adding this myself.
The bundled software is quite apologetic though.
Reason Limited (one of the best limited version daws I've used, still limited though), Ableton live 50$ coupon, AAS analogue, strum, Rhodes session (not very useful), korg m1 LE (useful for sounds of that era), ezdrummer lite, (useful) and UVI Digital Synsations (useful, retail price is $199.00)

19-MONTHS-OF-USE-EDIT:
After, on the side, using the akai lpk 25 for around a year and modifying it to decrease the deadzone greatly, I'm considering buying another nanokey, for much faster and more comfortable very fast monophonic triggering of notes.

Given the low price, I bought this controller on a whim. On taking it out of the box and giving the keys a quick play, I was immediately disappointed - the keys felt spongy and indistinct, with little tactile feedback. Connecting the device and loading up a softsynth told a different story; In spite of the poor key feel, velocity sensitivity is remarkably good and it is easy to play lines with consistent velocity across the full range. The keys work particularly well for drum programming, where a conventional keyboard action tends to fall down.

The pitch and mod buttons are a little pointless IMO, as they are simple on/off switches that don't seem very useful. The octave buttons are nicely designed, with a multi-coloured LED indicating the octave shift.

The included software bundle is very good and justifies the purchase price alone. You get Korg M1 LE, EZ Drummer Lite, a bundle of AAS session instruments, a lite version of Reason and a €30 voucher off any version of Ableton Live.

This keyboard would obviously be fantastically useful for mobile music, but I could also see it as being a good option for someone starting out in computer music on a small budget. I'm really taken with this little controller and can see all sorts of uses for it.