Jennifer Ehle, to begin with, is The Perfect Elizabeth Bennet. Witty, sparkling, attractive, and she has "fine eyes". :) I love the way she plays serious scenes--she switches from totally facetious to totally sober, and it's still believable. And she cries very well in the scene when she finds out about Lydia.
Colin Firth is perfect as Mr. Darcy! He is tall, dark and handsome. Colin Firth was for me, the definitive Darcy. He just owned the role and he looks good in a wet shirt too! ;)