At my friends place he uses Cubase and has Altverb. I have played around with it. It does have plenty of tweakability, it is easy to figure out.
An IR collection is readily available like as above true stereo high res IRs is what you want..
 
Any IR player can reproduce the IRs including Perfect Space.
If you figure out how to use Perfect Space it is nearly as good without the cost involved.
It is just Perfect Space requires some learning. It has plenty of control if you go deep.
 
You'd be surprised how good it is and at the end of the day you'd be hard pressed to use any more than 25% on a track or in a mix and more like 15-20% most of the time.
 
 

Altiverb works great and is a beautiful sounding reverb

It is. I'm just pissed they show no real intention of developing/supporting for Windows, yet have taken money from people four years ago, promising that a version 7 was forthcoming.

I think the simplest affordable option with proven support is IR-L by Waves, which is what I did. I wish Audioease was serious about Windows support, or failing that, that they wouldn't charge an arm and a leg for their older Altiverb 6 so that I could take the lack of support a little easier.

I've been looking into Liquidsonics Reverberate. It's a lot cheaper and is "true stereo". Reverberate Core is even cheaper and still "true stereo". They have a demo.
http://www.liquidsonics.com/home.htm

Oh also, Altiverb isn't available as 64 bit VST and doesn't work with Sonar's bit-bridge server. It needs some aggressive fiddling with jBridge (if you have that), as far as I've read. Just to underscore my point about support.

clintmartin
I've been looking into Liquidsonics Reverberate. It's a lot cheaper and is "true stereo". Reverberate Core is even cheaper and still "true stereo". They have a demo.
http://www.liquidsonics.com/home.htm

I think the main thing is still you need a nice library of IRs. It doesn't seem to come with any. Not as a criticism of the product, but if you're looking to replace Altiverb, one of its strongest points is the library (perhaps even more than the actual plugin).

Reverberate comes with 400mb of IRs and Core has 64mb. I don't have any idea how good they are. There are several online for free.
Here is a Reverberate comparison chart.
http://www.liquidsonics.com/software_reverberate_compare.htm
I don't own this and I'm in no way saying it even compares to Altiverb. It's just a lower cost alternative.

Oh cool, thanks, I totally missed that!

Altiverb works fine and needs no fiddling.  I have 32 bit Altiverb6 and works fine

Yes, I have and love AV6.. as stated, there is NO AV7 for windows. Usually, I don't bash a company but sadly, ALTIVERB has promised or hinted that AV7 WIN x64 will be available soon (still waiting after more than 3 years).
 
So, AV6 under SONAR x64, somewhat works but causes CRASHES running on both bit bridges, so I have abandoned using it.  I have replaced it with WAVES IR, not as many spaces but sounds OK... come to think of it, I don't use WAVES IR that much either anymore.  My new SPACE reverb of choice is the UAD Ocean Way Studio plugin if I can't recreate any space with reverbs and delays (which I probably do more than use OWS plugin).  I use a combination of EMT plate reverb and the old STUDER tape delay trick to create AIR and SPACE in a mix.  For music, DIR DRUM MICS samples have ZERO air, so I mainly use OH or ROOM ambient mic samples and only use the DIR drum kit samples for the transient and placement in the sound stage (left, center, right).
 
I am glad I wrote this response, I longer am that mad at Altiverb, cause I probably have replaced the use of IRs with old school mixing techniques.
 
So, a little off topic but I hope I helped the OP. to stay away from Altiverb until they finally release a WIN x64 version (which may never happen).
 
Jim