DJ mixers

Hardware

KORG Zero4: MIDI, Firewire audio, 4 channels, BPM-based sampling, effects, phono/line/midi/audio control, i.e. almost everything in one place (except deck control). Unfortunately, KORG discontinued the Zero4 (and Zero8) not long after they were introduced in 2007. The retail price was $1299. Glowing review: http://www.skratchworx.com/reviews/zero4.php This item is rare even on eBay. As of 2010-11-15, there are four for sale there, two from Japan and two from UK, all new in box. Example: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250727076468#ht_885wt_1010

Here's a page listing interesting fixes for problems with the Korg series: http://www.korgforums.com/forum/phpBB2/viewtopic.php?t=55865

Allen Heath XONE 3D: MIDI, built in USB sound card. Good for effects. Over $2500.

DENON DN-X1600: A four-channel digital mixer for USB, phono, and other audio sources. $1000. http://www.agiprodj.com/denon-dn-x1600.html http://denondj.com/DN-X600-P124.aspx
DENON DN-X1700 4 Channel Club Mixer with Effects. $1800. Sound and MIDI through USB. Also a MIDI out DIN-5 port.
DENON DN-X600 Professional 2-Ch Digital Mixer. $700. BPM, effects, MIDI through USB, external effects loop. Channel 1 and 2 can be assigned to midi, phono, or cd, or even mic. Compact, not many knobs. http://www.denondj.com/DN-X600-P124.aspx

Native Intruments Traktor Kontrol S4 System: $899.99. 4-channel mixer with all the Traktor software buttons laid out in real hardware. Only 2 channels of analog in, each can be line RCA or phono RCA. Mic input also. Obviously, best for integration with Traktor software, but little power of its own.

DJM-700: $1000. MIDI, USB, BPM, effects, 4 channels, each can be assigned to the left/right/neutral of the crossfader. http://www.agiprodj.com/pioneer-djm-700-standard-mid-range-professional-digital-dj-mixer.html

Rane sixty eight: $2600. Everything, overkill. Made for Serato Scratch. MIDI, 4 channel, lots of buttons. Can control two computers.

Vestax PMC-05ProIV: This unit mixes computer, CDs, and phonographs. Some of its controls are MIDI-assignable. It has 2 channels. Comes in red or black. Since it is not a sound card, just a MIDI controller, to get two channels of stereo from computer to this mixer, one also needs a multi-channel audio box compatible with the computer.

Native Instruments Traktor Pro: $99, Mac and PC. Traktor Pro accepts instructions from the mouse, keyboard, and/or MIDI, to mix four decks of music, with effects, a filters, eq, and a crossfader. It can browse through my iTunes library, although it frequently causes a disk I/O error with my external iTunes disk; I think I would prefer to move music files to the internal drive, or perhaps use the iPod playback feature (although it doesn't work with iTouch or iPhone).