I'm surprised to see Aida listed so many times. I didn't find the sets to be all that interesting. The tour was almost identitical with just a few cutbacks.
Other sets I enjoyed:
Jane Eyre (perfectly captured the "memory" effect)
Falsettos (great use of minimal design)
Proposals (did anyone else see this?)
Phantom of the Opera (hated the show, but it sure looked pretty)
The Scarlet Pimpernal (Loved the Fragonard-inspired backdrops)
City of Angels (black and white/color and "framing" devices)
Return to the Forbidden Planet (2001 UK Revival)
Cloudstreet (Royal National Theatre - How did this play NOT transfer to the Lincoln Center???)
Urinetown (again, excellent use of minimal design)
Sunset Boulevard
Cats
De La Guarda (not really sets, but excellent use of space)
I've seen many shows with pretty sets, but the above (and formentioned) actually stood out in my mind upon viewing.
"What can you expect from a bunch of seitan worshippers?" - Reginald Tresilian