DJ Chronic,
I'm not sure what your budget is. But if you're doing strictly hip hop, you may want to check out
the Korg Electribe series. There are three the Electribe-A, an analog modeling synth, the Electribe-R, a rhythm synth, and the Electribe-S, a sampler. They all include an octave-long pad to play the sounds (or beat the drum kits). The Electribes A and R are about $400. I think the Electribe-S is $100 more at $500. I checked these boxes out in the music store and for the price, they did some really amazing, wacked-out stuff that would go really well with a hip-hop and other beat-oriented production.
You spoke of horns and strings for your productions. Those needs sound like a more traditional sound box. If that's the case, and you really want a good all-around box with great "traditional" sounds (piano, electric piano, strings, guitar, horns, etc...), then I suggest looking into
the Roland JV 1010. It's a wonderful box for high quality all-around sounds and it goes for about $450 (if you shop around, you could get it for $399 - $425). The sounds are not really "dirty", which is usually a plus for hip-hop, but you can "dirty" 'em up while recording.
Rev E
P.S. the Korg Electribes have a built-in sequencer.