IMPORTANT: DON'T GET A SYNTH. Synths are often in the range of $500 to $2000 for a decent synth, while a midi controller is rarely over $300. I got what they said was their best model in, an Edirol PCR-300 for $250, and my friend who got a lesser midi controller paid $200. Midi controllers are generally cheap, so don't get a synth, seriously. If you go into a clear, be clear about that because they'll try and rip you off if you just want a keyboard with midi exit.
Anyway, I'd recommend the Edirol PCR-300. That's what I'm using, and it works really fine with Fruity Loops. Fruity Loops is extremely hardware friendly so there's not much configuration to be done (except of course changing the nature of the midi signals if necessary (like buttons to hold, toggle or count when pressed etc)). Edirol is a Roland product so you could look it up. Also remember that having a wide range of keys isn't necessary since you can easily jump up and down between octaves. Only get one with a wide range if you plan on performing live (why would you perform live with a midi controller, though?).
But yeah, I recommend the Edirol PCR-300 by Roland. The end.