Mine is...

There are way too many to choose from, but Daniel Day-Lewis and Heath Ledger are definitely my top two favourites.

if everyones a character actor, then where are all the characters at?

Gary Oldman
Heath Ledger
Benicio Del Toro
Phillip Seymour Hoffman
Peter Lorre
Christian Bale
Jim Carrey
Cate Blanchett
Johnny Depp
Jessica Chastain (for the moment I have a crush on her acting abilities)
Audrey Hepburn (she did some amazing character acting in the past so I'll just mention her)

and few others who did character work but are not character actors...

RIFA wrote: Jessica Chastain (for the moment I have a crush on her acting abilities)

Easy to hop on the bandwagon.

Brad Pitt

IWatchFilmsNotMovies wrote:Brad Pitt

lol