All depends on your taste....
I find that the classic Chanel men's scents (pre-Platinum Egoiste) work wonderfully as formal scents.
If you're looking for something sweeter, L'Instant de Guerlain Pour Homme is an excellent formal scent.
The Third Man by Caron is classy and timeless.
Bulgari Pour Homme (the original) is a wonderful inoffensive formal scent, I believe. Extremely pleasant.
If you want to smell fresh and clean, Cacharel pour L'homme or Mugler Cologne both smell very dapper.