Hre
I was seriously thinking of the HRE C20 in a 19". This is a very light wheel that should reduce unsprung weight (compared to other 19's) and thus improve handling. They look good too.
One thing to consider is that every pound shaved off of the wheels is equivilant to about 4 pounds elsewhere on the car due to the effects of inertia and centrigual force. If you upsize to 19's, I would do some close checking to ensure that the new set up does not add weight - it seems that a lot of race cars actaully use 18's because they are lighter and stronger. That is why the HRE's were the logical choice.
Considering that the HRE's cost about $7500 per set, I eventually elected to stick with my stock 18's (ball finished with the vintage package). I think that they have a classic look that really complements the car plus their offset and design makes them pretty resistant to bent lips from road irregularities. Our roads here in Calgary are crap so I think going to a lower profile tire would be problematic for ride quality anyways.