I just wrote this on another thread today:
Has already mentioned, you really want to hear the DP in Stereo if possible. Both live or at your home/studio.
Active PA type speakers I think are the best way to go. For gigging, the "keyboard amp" is the most convenient but also sacrifices on sound quality. I've tried probably every conceivable amp and speaker combination over the years to best try to optimize the sound of my keyboard/DP. People go out and spend 2-3K on a keyboard like the Yamaha Motif 8, plug into a Berinnger or Roland KB amp and wonder why it sounds like s..t I would spend more dough on the sound system personally.
Currently I use for my stuff the EV SXA 360s active speakers. It's a 2 way, 12" and horn. For its class---weight/price/sound I think they are the best thing going. Expect to pay around $1600-1900 for a new pair. I run them into an older Mackie 1202 VLZ mixer, not the greatest high end piece of gear sonically speaking, but has great build quality, is super reliable and definitely does the job. Also has mentioned, the style of music and your volume level comes into play. The EVs can cover all the bases from Jazz solo/trio piano stuff to crankin' Rock-R&B. If you can, spend the dough on good speakers--in this area you really get what you pay for.
I don't play DPs at home very often but for recording I have a pair of the Dyn Audio BM6As MKII. The few times I've run my keyboards through them they sound probably has good has they will sound. Has mentioned you can't use studio monitors live though. You'll probably blow them up by overdriving them trying to compete with the drummer or bass player. They aren't meant for that purpose.
I also still have the Motion Sound KP-200 stereo keyboard amp. It sounds very good for "keyboard sounds" such has Rhodes, Clav, Organ and misc. synth stuff but it really doesn't make it for AP sounds---very harsh and srident. If you really hate patch chords and plugging stuff in plus like to get in and out of the venue has quickly has possible, this way can't be beat, although has mentioned , you are sacrificing sound quality especially on the AP. Then again some people aren't has picky has I am and the amp suits them fine.
So to sum it up--for live a good pair of active speakers and a small mixer.
For home/studio--a good pair of active studio monitors.
I was just checking the price on those EV SXA 360s. Someone on the Keyboard Mag Forum mentioned EV dropped the price on those. Evidently that's the case because the advertised "street" price is now $1600. I paid just under 2K out the door a few years ago and I shopped that deal like a madman.
A few brands I've owned or tried:
JBL Eons 10"s & the 15"s
Mackie SM-450s and SM350s
Acoustic Image Coda/Corus/ and the new Ten2
The older QSC--the HPR 122i I think it was. Haven't tried the newer QSC K series--the 8", 10" or 12"s. A lot of people on the aforementioned Keyboard Corner Forum own these and really seem to like them. Many threads over there on this subject.http://forums.musicplayer.com/ubbthreads.php/ubb/postlist/Board/18/page/1