Numa Compact 2 : It's not perfect, but it's what I was looking for.

This instrument has almost everything I wanted:

- USB/Midi

- 7 octaves

- Own collection of sounds

- Versatile

- Not expensive

- I would have wanted full weighted keys, but that comes with a price. So I settled for this capable semi-weighted action. In retrospect, I'm happy with my choice: I'm not a piano player, though I love the piano, I'm more of an allround, if not mediocre, keyboard player, so this fits very well.

It's very lightweight (maybe too much, the build construction leaves some doubts), and compact: it takes the space of the 88 keys and not much more.

The built-in speakers are a bonus, you probably cannot use them in serious environments, but to play around without connecting anything else than the keyboard, they're ok.

If you're not sure, there are many reviews on the internet to make up your mind, and the ones here helped me (thanks everybody!). If you're looking for something versatile, capable, lightweight and not expensive, this is a good choice, I'm very happy with it.