It's already said and done I guess...
But I'd have to agree with Keb that the Verbzilla is the way to go. I'm a big reverb user, and I've tested out most of the stuff mentioned (with the exception of the digiverb.) My favorite by far was the Verbzilla, followed closely by the EHX Holier Grail. Both of them are a tad more expensive than the RV-5 or the Holy Grail...but the RV-5 sounded really sterile to me, and two of my friends had Holy Grails that crapped out on them. The Holy Grail sounds great, but I've also heard a lot of complaints about noise issues.
And the Holiest Grail just seems like overkill.
EDIT: And if your into some more experimental, weirder noises, Definitely the verbzilla. Some of the settings on there are so gnarly...it's pretty sweet. I'm a fan of that David Gilmour cave reverb, and the verbzilla definitely delivers that, plus a lot of great extras.