Sites marked SE are in Swedish, the others are in English or have an English version.

Forums and groups

Language of adaptive music, Yahoo group on adaptive music theory.
IASIG, Interactive Audio special interest group.
Project BBQ - "The Premier Interactive Music Think Tank"
Game Audio Network Guild
InteractiveSound.org

Academia and institutes

Interactive Institute, Sweden
KTH Speech
IRCAM
CCRMA

Misc.

Java Music Specification Language, with some algo music demos
Wolfram Tones

Articles

Defining Adaptive Music, (Gamasutra 2007 april 17)

Books

George Sanger: The Fat Man on Game Audio: Tasty Morsels of Sonic Goodness
David Cope: Experiments in Musical Intelligence

Game Audio Middlewares and Tools 

FMod
SoundMax

Synths, Samplers and Sounds

Propellerhead Software
Native Instruments
East West Samples
Garritan 
Clavia

Midi

Midi Manufacturers Association, midi.org
MidiYoke, virtual midi cables
Midi-ear, audio to midi capture

Sequencers and plugins

jVSTwRapper, The Java Way Into VST World

Java vs. C++ performance (Killing the "Java is slow" myth)

Performance roundup

Musicians forums

Vi musiker SE

Gaming forums

Game Elite, SE

Network

IQube, SE
ALMI, SE
Vinnova, SE
Innovatum, SE
STING