Depends on the opponent
Thompson: Iowa, Ohio, New Mexico, Colorado, Florida
Romney: West Virginia, Arkansas, Ohio, possibly Florida
Giuliani: Iowa, Ohio
McCain: Iowa, Ohio, New Mexico, Colorado, Florida
My take:
Thompson: West Virginia, Arkansas, Iowa, Ohio, New Mexico, Colorado, Florida, Nevada
Romney: West Virginia, Arkansas, Iowa, Ohio, New Mexico, Colorado, Florida, Nevada
Giuliani: West Virginia, Arkansas, Iowa, Ohio, New Mexico, Iowa, Ohio
McCain: Arkansas, Iowa, Ohio, Colorado, Nevada
I don't know why so many are overlooking Nevada, considering it was basically the national average last time.