oh please, there is only one correct answer to this thread.
SIR 1.008
the best reverb plugin. full stop.
why?
1) its a convolution reverb VST plugin and its 100% free.
2) there are impulses recorded for it from famous (and expensive) outboard gear like the lexicon PCM91 as well as various selections of of plate reverbs and impulses recorded from real spaces.
3) all of those impulses? they are free too. go check out
www.noisevault.com
4) SIR can import any wav in order to use some of its properties. it is more than just a reverb plugin.