I like Waves Renaissance Verb when I mix in the box - you can edit a lot of it's settings and it just sounds good, like a majority of the plugins that Waves has to offer.

Ditto on the Renaissance verb, also Waves Truverb and Trueverb m/s.

The two most popular have been mentioned, I guess, though you should feel free to use whatever sounds good.

To improve quality you can combine the two to get a denser reverb tail. Quality of a reverb is partly determined by the tail. And don't forget to experiment with a little delay and doubling(very short delay).

Now it's up to you to decide whether if one reverb triggers the other or if they are in parallel, same with the delay.

ALTIVERB

I have got T600 IR and IMHO it smokes every native plugin I tried.

http://www.samplicity.com/

Amazingly well done. Peter Roos did awesome work.

Altiverb is also the first class if you like natural room reverb.