i already an an sp303 and an sp404sx. i found the 606 in a pawn shop for $250 dollars. what do you guys think of the 606, and how much does it usually go for?

the best use for the 606 is with a pc: it was conceived for that aim; think of it as a pioneeristic anticipation of NI Maschine and more: it's a sampler, a soundcard and a midi controller; it has synth and fx inside and sensitive pads; it sounds well (according to the master function); it has also usb storage function, it has a real/step sequencer
BUT
the sequencer doesn't sends midi "hardware" notes, just "software" midi notes.
you cannot resample patterns on standalone (you can with p606 soft)
doesn't have real pitch (the same as above)
you cannot memorize fx set up
it isn't upgraded to win7 (and more)

If the 606's is in good condition, $250 is a good price for what its capable & compared to what's also out there (ie- Maschine).

If you do buy it, don't sweat missing the manual & P606 program. You can get the manual here: http://www.roland.com/support/article/?q=manuals&p=SP-606. If you get in touch with Roland, chances are they'll be cool & send you the P606 program. P606 is OK, but if you already run a DAW you may as well use the SP606 as a sound card & sample from that instead.