Audiomulch is my VST host of choice. Unlike many VST hosts, it is completely modular, allowing you to chain your plugins together in any way you see fit, without forcing you to work in a "mixing console" metaphor.
K-v-R is the place to go for VST and other software synthesis news.
The Music-DSP Source Code Archive is a good place to exchange information about developing audio synthesis/processing software. There's also a Music-DSP mailing list. And a Music-DSP Wiki.
...more to come...