Virtual Instruments and Effects

http://www.voxengo.com/product/tubeamp/
http://www.puremagnetik.com 
http://www.soundsonline.com/ (East West Quantum Leap)
Steinberg Halion Symphonic Orchestra

Drum Loops:
http://www.groovemonkee.com/en/products 
http://www.oddgrooves.com/loop-shop/jazz-drum-loops-swing-midi/ 
http://www.synthzone.com/drums.htm

Piano:
http://www.soundiron.com/instruments/pianos/emotional-piano/

GUITAR: 
http://www.ilyaefimov.com
http://8dio.com/?btp_product=songwriting-guitar

Percussion:
http://www.applied-acoustics.com/chromaphone/overview/ (BASS MARIMBA!)

For mixing with headphones:
http://112db.com/redline/monitor/
http://www.toneboosters.com/tb-isone/
http://www.focusrite.com/products/audio_interfaces/vrm_box/

Stereo Enhancement
http://nugenaudio.com/stereoizer.php


Companies:
http://www.sonokinetic.net/
http://www.soundiron.com/
http://cinesamples.com/
http://8dio.com/
http://www.imperfectsamples.com/
http://samples.wavesfactory.com/
http://www.kirkhunterstudios.com/index.html 
http://www.beladmedia.com/ 
http://www.store.precisionsound.net/about.php 
http://www.hauptwerk.com/ (modelled pipe organ) 
http://www.hollowsun.com/ (Mellontron)

Selling sample instruments:
http://www.sampleism.com