Hello,

This is provided without any particular order (except for MotU being at the top as I do particularly dig them). I have tried and used all of the products below, though I won't claim any profound expertise. Some of the lower-cost vendors provide incredibly high-quality products, so one can get a lot of bang for the buck nowadays:

Iver

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MotU: Mark of the Unicorn

http://www.motu.com/

Digital Performer: one helluva tool

MachV: a dynamite sampler, though I wind up using Kontakt (see below) more often
MX4: great and flexible synth
Orchestral: dynamite orchestral instrument...nicely complements others too
Ethno: just getting into this, a very handy sampling of ethnic instruments

Audio Interfaces: probably the best bang for the buck out there
2408 mkIII: great workhorse
24I/O: plug all those synths directly in!
MotU also makes lots of standalone FireWire interfaces (i.e., that don't use the "PCI-424" interface) but I haven't tried them

MIDI Time Pieces: the best MIDI interfaces
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Digidesign Pro Tools

http://www.digidesign.com/

The 800lb. gorilla of recording. A subdivision of Avid. Great stuff but, in my opinion, incredibly finicky and demanding as regards system resources. Also incrediby expensive if you get into the HD stuff.

However, PT is ubiquitous so one should at the very least be familiar with it and aware that you may have to transfer files to/from Pro Tools.
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Waves:

http://www.waves.com

The 800lb. gorilla of plug-in effects. Super clean stuff and arguably the basic toolkit for processing. Not inexpensive.
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UAD (Universal Audio)

http://www.uaudio.com

A great card for offloading effects processing from the computer's CPU. Excellent sounding stuff!
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TC PowerCore: another way to offload processing to a card

http://www.tcelectronic.com

http://www.tcelectronic.com/PowerCoreConcept

Virus: runs on PowerCore, sounds fabulous
Novation V-station: I really dig it
Sony Oxford plugins: very high quality
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LinPlug: very cost-effective and very nice.

http://www.linplug.com

CronoX3: atmospheric and great for sound design
Octopus: extremely flexible FM-like synthesis...I'm just scratching the surface
RMIV: drum module
Albino3: if you were to get just one soft-synth, this could be it
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Rob Papen

http://www.robpapen.com

Blue: very, very nice and flexible: more moody (to my mind) than Albino or Octopus, but very cool
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Spectrasonics

http://www.spectrasonics.net

Trilogy: bass samples...great bass module
Atmosphere: various pad-like samples, super-handy and great sounding
Stylus RMX: kick-ass remix tool
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Applied-Acoustics

http://www.applied-acoustics.com/index.php

Lounge Lizard: super-nice electric piano
Tassman: sound-design monster
String Studio: very cool string instrument emulation
Ultra Analogue: great analog synth emulation
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PSP Audioware

http://pspaudioware.com/

Great-sounding, very reasonably priced effects

Vintage Warmer
PSP Nitro

PSP 608 MultiDelay or the Lexicon PSP 42 and 84 for an actual hardware emulation. The 608 is a monster
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Nomad Factory

http://www.nomadfactory.com/

Great sounding effects...I think "Blue Tubes" is wonderful
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Audio Ease

http://www.audioease.com/

VST Wrapper: handy way of using VST synths in an AU (or MAS, like Digital Performer) host

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Elemental Audio/Roger Nichols Digital

Roger Nichols is now selling the Elemental Audio plugs

http://www.rogernicholsdigital.com/
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Celemony

http://www.rogernicholsdigital.com/

Melodyne is an amazing pitch-correction tool
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Audio Damage: very reasonably priced effects

http://www.audiodamage.com
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DB-Audioware: very interesting effects

http://www.db-audioware.com

QFX can do amazing things
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Native Instruments

http://www.native-instruments.com

FM8: like a DX on steroids
B4: very cool Hammond emulation
Kontakt: dynamite sampler
GuitarRig: integrated interface for guitar recording
Absynth: sound-design and synth monster
Elektrik Piano: another great electric piano...this one based on samples as opposed to Lounge Lizard
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Korg Digital Legacy: those great old synths in software!

http://www.korg.com/gear/info.asp?A_PROD_NO=KLC1D
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Arturia; great emulations of legacy synths

http://www.arturia.com/en/default.php

MiniMoog
Moog Modular
Yamaha
Sequential Circuits
Brass

Arp2600V
Moog Modular V2
MiniMoog
Yamaha CS80V
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Propellerheads

http://www.propellerheads.se/

Reason: standalone and Rewire compatible host
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GMedia

http://www.gmediamusic.com/

Imposcar
Oddity
M-Tron
Mini-Monsta
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Camel Audio

http://www.camelaudio.com

Cameleon 5000: zany sound-design monster
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BIAS Peak: the standard audio editor

http://www.bias-inc.com/
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DSP Quattro: very cost-effective and high quality editor

http://www.i3net.it/Products/dspQuat...p/Index_EN.asp