Today I randomly stumbled across Wikipedia's list of Secret Service codenames from the mid-50s to the present. President-elect Barack Obama is known as "Renegade." (Which is sort of like "Maverick," but better.) His wife and daughters are called "Renaissance," "Rosebud," and "Radiance."
One guy who clearly must have done something to irritate the Secret Service, though, was Gerald Ford's press secretary, Ron Nessen, who was known to the Secret Service as "Clam Chowder." Come to think of it, dude seems to have had a pretty wicked sense of humor, so maybe he got to pick his own. Nessen was the first political figure to host Saturday Night Live during its first season in 1975. You can read transcripts of some of the sketches in his episode here. Unfortunately Nessen as Jefferson's press secretary in "Press Secretaries Through History" hasn't yet been transcribed.