Sorry if any of these have been mentioned, but:
Sigourney Weaver and Michael Beihn
Whoever would be good at playing an adult Newt
Samuel L. Jackson
Harrison Ford
Daniel Craig
Michelle Rodriguez
Bruce Willis
Sylvester Stallone
Adrien Brody
Alice Braga
Arnold Schwarzenegger
Danny Glover
Dwayne Johnson
Chuck Norris
Pierce Brosnan
Jean-Claude van Damme
Steven Seagall
Laurence Fishburne (seriously, bring Noland back somehow, his death sucked)
The villains:
Lance Henriksen
Adam Baldwin
Charlie Sheen
Garey Busey as Android Peter Keyes!!!