PowerTracks Pro Audio 5.0
Features up to 48 tracks of digital audio with effects, EQ, and panning plus 3rd party plugin support.
http://www.powertracks.com/

Data Sonic
VSPro is a Win95 sequencing and notation package with a full graphic interface for Roland VS880 control and integration.
http://www.datasonics.com.au/

Personal Composer
Music notation, MIDI sequencing and publishing program.
http://www.pcomposer.com/

n-Track Studio
Multitrack recording program offers realtime effects via DirectX plug-ins, has audio and MIDI tracks.
http://fasoft.com/

Z.Matrix
Surround-panning plug-in for any MIDI sequencer that supports SCOPE/Pulsar. Simulates up to 16 sound sources from freely placed speakers.
http://www.zmatrix.de

Sonic Network Inc.
Soundfonts, some for free. Many sequencers support soundfonts.
http://www.soundfontsamples.com

Making Waves Audio
Multitrack MIDI, loop, and FX sequencer.
http://www.makingwavesaudio.com

Ntonyx
Style enhancer processes MIDI files to add human performance characteristics. Stand alone version and Cakewalk plug-in.
http://www.ntonyx.com/

MultitrackStudio
Audio/MIDI recording and mixing environment for home recording musicians.
http://www.multitrackstudio.com

Griff Pocket Music Studio
Sequencer for PocketPC running Windows CE. Sampler, instruments, and effects also.
http://www.planetgriff.com/

Quaderno
For MIDI sequencing and to aid musical composition and research. Some unusual options.
http://www.quaderno.com

FL Studio
Fully featured sequencer with MIDI, VST/VSTi and DXi support. Can be used inside other sequencers as a VSTi itself.
http://www.fruityloops.com/

Propellerhead Software
Creators of the popular Reason, ReBirth, ReCycle software packages.
http://www.propellerheads.se/

Sonic Syndicate Software
Creators of the Orion audio sequencer.
http://www.sonic-syndicate.com/

Woltec.com
Music creation tools including Quartet X2 Music Studio.
http://woltec.com/

Ableton Live
Audio sequencer playable in real time like an instrument. User area, support, company profile, purchasing.
http://www.ableton.com/

PC Drummer
Create drum music for less than the cost of a physical drum kit or machine. Built-in sounds sampled from actual instruments.
http://www.pcdrummer.com

Easy Music Composer
MIDI sequencer for Windows.
http://www5f.biglobe.ne.jp/~mcs/emc.html

GrooveMaker
[Mac - Win] Loop based mixer and sound libraries, with real time groove-generator and import/match of any audio file, including MP3.
http://www.groovemaker.com/

Zynewave Podium
Audio/MIDI sequencer integrates multitrack recording, external hardware, and VST plug-ins, using a hierarchic mixing engine. Windows.
http://www.zynewave.com

Kyma
Symbolic Sound Corporation's Kyma is a graphical language for live, interactive sound generation and manipulation.
http://www.symbolicsound.com

Rosegarden
A professional audio and MIDI sequencer, score editor, and general-purpose music composition and editing environment for Linux.
http://www.rosegardenmusic.com/

Anthem
An advanced open source MIDI sequencer for Unix-based platforms.
http://anthem.sourceforge.net/

Tracktion
[Mac - Win] Audio and Midi recording and editing software from Mackie. Main features, screenshots, reviews, documentation and support area.
http://www.mackie.com/products/tracktion/

Midish
A simple and lightweight command-line MIDI sequencer/filter for BSD and Linux.
http://caoua.org/midish/

KinTools
Freeware sequencer allows movement of sound among multiple speakers. Speaker control can be applied to other programs.
http://www.kineticsoundsystem.com/

Storm Music Studio
Description and features of this program from Arturia with virtual instruments, sequencers, synthesizers and effects.
http://www.arturia.com/en/storm/studio.php

LMMS
Open source sequencer for Linux.
http://lmms.sourceforge.net/

SQ4²
Controls your external gear through MIDI, controls VSTI's.
http://www.webgenpro.be/www.sq4.be/

Digital Orchestrator Pro
Voyetra's flagship digital sequencer.
http://www.voyetra.com/site/kb_ftp/160ftp.asp?wb=1

WiseMix Ltd.
Offers MCmu, an MCU emulator for Windows.
http://www.wisemix.com/

Breakage
Artificially intelligent drum machine with breakbeat composition employing neural networks and morph functions.
http://www.blackholeprojector.com/

Band-In-A-Box User Group
A Yahoo Group for PG Music's Band-in-a-Box MIDI based music program. Swap files, styles, and get help.
http://groups.yahoo.com/group/Band-in-a-Box/

Syntrax
Mobile music studio for your PocketPC, offers software synthesis, sequencing, and sample editing. Desktop version also.
http://www.finished.nl

Making Waves Software
Offers Audio 5 and Studio 5. Demo available.
http://www.makingwavessoftware.com

AuReality
Offers controller remappings, LFO's, arpeggiators, autochords, drum and note sequences, and echoes.
http://aureality.midiworld.org/

Deck
[Mac] Multitrack audio and Midi sequencer: screen pictures, main features, reviews, downloadable demo.
http://www.bias-inc.com/products/deck35/