Ambience is recommended to me by my producer friend a few years back, and honestly, it is one of the best good reverb plugins for free.
One of my favorite features of Ambience is the hold parameter which smartly freezes the reverb tail until the button is released. You can use this for creating a reverse reverb effect, special effect and you can even automate the knobs.
Ambience is a donationware plugin. You get a nag screen with no limitation, and if you love the plugin, you can donate to the developer.’
Download: Win 32 VST / Mac OSX VST