You really need to just try some out. 
 
Tastes and needs differ too greatly among users.  The sound design guy who needs the power and depth of 2cAudio's Aether wouldn't be satisfied with just the Valhalla verbs -- as great as they are.
 
Vice versa, the guy who's only used his DAW's stock reverb would be overwhelmed with Aether.... but might find Breeze (also 2CAudio) the perfect step up.

I have Reverberate 2 with the Bricasti stereo IRs and I think it does all the big spaces well enough.
Valhalla room is nice too.

REmatrix sounds gorgeous.

Yes, I picked up REmatrix for $99 on a group buy. Nice plug-in. From the man responsible for many of the algorithms in Lexicon hardware reverbs Exponential Audio gets good reviews.

Valhalla are pretty inexpensive and excellent, both as natural and "effect" reverbs. Very light on system resources as well.

Overloud's Springage is a good spring reverb emulation. Not quite as warm, boingy and Neil Young/Dick Dale as my '63 Fender reissue valve reverb, but a quite acceptable substitute. And stereo, unlike the Fender.

Waves' I'm not so keen on for reverb. Nothing particularly poor about their reverbs, just that there are others I think are better and cost no more or less than Waves.

Though the reverbs that come with Platinum and earlier verions of Sonar are all somewhere between good and very good.

Thanks to everyone for sharing your go tos.  I'm definitely going to check out Valhalla's offerings. 
 
Several of you mentioned the Lexicon PCM Native, and as I looked around on the interwebs, it seemed that many out there think it's one of the best.  "Sounds just like the hardware", which is a good thing - especially since it's the hardware I'd be looking at if I weren't in "sub-$1k" land.
 
The most common complaint was the price.  This package used to be priced pretty high, even the ~$600 street price is more than I would want to spend - too close to to $1k.
 
It seems that Sweetwater has the PCM Reverb Bundle for $299 this month, which is still high for one plug, but comparable to the waves stuff when they're not on sale.  Still, its comfortably sub $1k.
 
I'm thinking about pulling the trigger on the Lexicon, will I need an iLok?  I've heard bad things about iLok over the years, have they worked things out?

BTW - No longer considering Waves H Reverb.  Y'all saved me $150.

Depending on your needs, one may want to investigate ALTIVERB.  Yes an IR based system but the absolute best IRs in the world (you can only use them with AV) and they are part of the system.  You get all the existing and any new IRs that they produce and they have TONS of them and they do sound quite good.
 
Most think that AV is used for VIDEO production spaces but these IRs are also quite musical.  Not only do they have IRs of real spaces (and I mean a ton of real spaces) like studios and concert halls but they have quite a few hardware IRs that are quite good as well.
 
If interested, check out the Audio Ease website for a breakdown of what this system is about.  I love mine even though I have the UA stuff as well.  My goto is probably the UA EMT 140 plate but I also use the real spaces of AE for AIR in mixes.  It works great.
 
Jim

+1 for Valhalla reverbs. I have Room, Plate and Vintage and they all have their place. However I have two other go-to reverbs and those are the Softube RC-24 and RC-28 that come in Komplete (Ultimate?) and are sold by Native Instruments separately in their "Reverb Classics" package. Both beautiful and versatile sounding reverbs with a very wide range of flavors. 
 
If I wasn't trying to drastically cut down my spending on plugins though I think I would have bought Altiverb a long time ago. I literally (not literally) drool whenever I hear examples of it. 

Altiverb is still on my list too. One of those things that I know is great but I can't really justify the high price. Kinda like I had with Melodyne. So maybe Cake can help us get started again :D