Bill-
This is a great post to live vicariously... and think about all the money I'm saving by not going....
If money isn't an object....and it sounds like it isn't... then I'd vote for a float trip for Mongolian Taimen or Kamchatka steel head for something really exotic. Seychelles bonefish, Amazon peacocks, NZ, or an Alaska float sound cool too though perhaps not as exotic as your clients are looking for.
Here's one that I think would be a blast, and I hope to do one day (Fishing for Nile Perch in Eygpt). They mostly use conventional tackle, but it looks like it would be a hoot with the right fly gear: http://www.african-angler.co.uk/ I think Larry Dahlberg did a trip awhile ago. They can apparently customize trips too, in addition to their packages.
And there's always a pack trip into the Bob Marshall...
best of luck... can't wait to hear the stories and see the pics!
peregrines