Bootsy freeware pack is good place to start
KVR: bootsie roundup

from commerical plugins i really like all stuff from Stillwell Audio
Audio Plugins | Stillwell Audio - It's About The Sound

for saturation IK Amlitube is great. I love AmpegSVX for bass saturation. Jimi Hendrix and Metal are both nice for screaming tones.
KVR: Audio Plug-in Database (Search Page) - VST, Audio Units, DirectX, LADSPA, DSSI