Figure out the type of crate you will need. If it's for home use, choose a heavy gauge wire crate for the best ventilation. Wire crates also provide a better view for your dog and facilitate more interaction and socialization. If you will be storing or moving it often, a collapsible model with handles that can be easily folded down into a "suitcase-style" shape will work best.
The following is a good guide:
Extra small: Pomeranian, Shih Tzu, Chihuahua
Small: Boston Terrier, Jack Russell, Yorkie, Maltese
Medium: Cairn Terrier, Cocker Spaniel, Llasa Apso, Dachshund
Large: Basset Hound, Bulldog, Welsh Corgi, Shar-Pei
XLarge: Chow, Collie, Dalmation
XXLarge: German Shepherd, Greyhound, Golden/Labrador Retriever