Audio Damage's Automaton

Automaton is a VST / AU for stuttering and altering your music inside your DAW of choice. It's $49, and you can check out some examples of how it works on the Audio Damage website, or watch videos of it in action, such as these two from youtube:

Free "mnml" loops and samples from mimu

mimu have a stack of free sound packs for those who need loops and samples to play with. There's glitchy stuff and circuit bending noises too.

Forester

Forester is free software for OS X and Windows which will help you remix, glitch and basically make interesting music in general.

And Even More Glitch VST's

2 Rule Filter by 2 Rule (Windows only?) FREE!

Daft Funk by Klanglabs (Windows) FREE!

Glitch by Klanglabs (Windows) FREE!

Truc by de la Mancha (Windows) FREE!

Pudding by TWEAKBENCH (Windows) FREE!

Sideslip by TWEAKBENCH (Windows) FREE!

InstaJungle by Laurence Davies (Windows and OSX) FREE!

Scuzzphut6.5 lite by Scuzzphut (Windows only?) FREE!

Ring Thing by de la Mancha (Windows) FREE!

Even More Glitch VST's

Ultrabeat in Logic 8 (OSX)

Stylus Remix by Spectrasonics (Windows and OSX)

iZotope Spectron (Windows and OSX)

CamelSpace by Camel Audio (Windows and OSX)

Beatfckr by Cees Taal (Windows) FREE!

More Glitch VST's

Ultra Trigga FX by AZ Audio (Windows) FREE!

Dead Beats by Scott Monteith (Reaktor) (you can get this one free here)

Live Cut by Smart Electronix (Windows and OSX) FREE!

Effectrix by Sugar Bytes (Windows and OSX)

Shattersync by Pluggotic (Windows) FREE! (Based on Shattershot Lite by DarkWare)

Konkrete and Konkrete 2 by Soniccouture (Kontakt)

Glitch VST's

dBlue Glitch by Illformed (Windows) FREE!

Buffer Override by Destroy FX (Windows and OSX) FREE!

Replicant by Audio Damage (Windows and OSX)

Toxonic Glitch by Joachim Schneider (Windows and OSX but only with Reaktor) FREE! but you must be registered.

Major Malfunction by Defective Records (OSX)