(note: I haven’t actually got anything to compile yet, these are just some notes, will update later…)

Steinberg’s free VST SDKs with bullshit restrictive license:
http://www.steinberg.net/en/company/3rd_party_developer.html

to bypass Steinberg’s required registration, which is currently broken:
http://www.bugmenot.com/view/steinberg.net

DEVCPP (free GCC IDE):
http://www.bloodshed.net/dev/devcpp.html

how to set up DEVCPP to compile VST (edit: or my easier-to-read PDF version)
http://www.u-he.com/vstsource/files/vst_with_dev_c.txt

VST.NET, open source implementation that does not require the Steinberg’s SDK (I think):
http://www.codeplex.com/vstnet