here are a bunch of nice freebies that i regularly use:
ANALYSIS:
-Voxengo SPAN for Spectrum Analysis
-Flux Stereo Tool for Stereo widt & phase analysis
-Stillwell Bitter to check bitdepth
-Smartelectronix s(M)exoscope to have a look at the Waveform
-TT Dynamic Range Meter to check how loud things are
FX:
-Xfer OTT - nice little multiband dynamics thing similar to the one in ableton live
-Flux Bittersweet & Sleepy Time Transient for Transient processing
-Voxengo's MSED to make things wider/more narrow and for M/S de-/encoding
-iZotope Vinyl for some vinyl ambience
-SIR for impulse response reverb
-Glitch - an all in one FX unit
-the NI Players package for all sorts of things incl. Guitar Rig 4 Players
-Smartelectronix PanCake 2 for stereo madness
-CamelAudio CamelCrusher (i've heared they shutdown their site, so might need
to search a bit for this one)
-Sonalksis FreeG (simple gain fader)
-Tone Projects Basslane to mono the low-end
-Smartelectronix Ambience for Reverb
VSTi:
-Synth1 (is even used by noisia)
-Eclipsis by VST Zone
this is just a little selection
....there are countless free VSTs all around the web and featured on countless
websites and blogs - just have a quick google search and btw: don't DL all sorts
of useless crap cuz you won't need/use a lot VSTs anyway. i know a lot freebies that
are poorly coded and make your DAW crash - get a nice little selection, make
sure the plugs work and learn them inside out (PDF manual...) - everything else
just uses up unnecessary hardrive space and takes ages to load...
hope that helps