I have to concur with both 2001 and Baraka, both look absolutely stunning on Blu-Ray. In fact in 2001 you can actually see the paintbrush marks on the painted backdrops in the Dawn of Man sequences. (It doesn't detract in my opinion.)
The Ghostbusters transfer is fairly poor I thought, but most films I've seen have had pretty good transfers. Master and Commander had a huge amount of ghosting in it, but that might have been a fault on the disc I rented - it looked pretty dirty.
Films I'm looking forward to revisiting on Blu-Ray (off the top of my head): Akira, Get Carter, Taxi Driver, Schindler's List, Seven Samurai, The Wicker Man.
I'd love to see a high-res version of Mick Jackson's Threads, but I seriously doubt that'd ever happen.