Checkout the Novation K-Station. It's a very reasonably priced synth and it has great sounds. It has a vocoder and audio input as oscillator which means you can create some very unique and interesting effects. You could for example feed the output from a sampler or other synth to the audio in.
The ultimate synth in my books, is the Novation Supernova 2. It has a 40 band vocoder and extremely powerful synthesiser.
If I had to choose between K-Station, Korg MS 2000 or Microkorg, I'd go for K-Station (it has more voices as well!). Novation have a new synth out now so you can check that out as well.
:-)
Feathers.