From Wikipedia:

ca. 1994 - Ron Gomez, former member of the Louisiana House
1994 - Walter B. Jones, while running for U.S. Representative from North Carolina
1994 - Ed Whitfield, the day before filing as a candidate for the U.S. House in Kentucky
1994 - Ron Gomez, former member of the Louisiana House of Representatives from Lafayette switched to Republican after unsuccessful campaign for Mayor of Lafayette in 1992
1994 - Mike Bowers, while Attorney General of Georgia
1994 - Fob James, while running for Governor of Alabama
1994 - Richard Shelby, while U.S. Senator from Alabama switched on November 9, 1994[6]
1994 - Woody Jenkins, while Louisiana state House member
1994 - Dan Richey, former Louisiana Democratic state legislator switched from Independent to Republican when the Republicans won control of the U.S. Congress
mid 1990s - Ed Austin, while Mayor of Jacksonville
1995 - Jimmy Hayes, while U.S. Representative from Louisiana
1995 - Greg Laughlin, while U.S. Representative from Texas
1995 - Ben Nighthorse Campbell, while U.S. Senator from Colorado, switch March 3, 1995[7]
1995 - Billy Tauzin, while U.S. Representative from Louisiana
1995 - Nathan Deal, while U.S. Representative from Georgia [47]
1995 - Mike Parker, while U.S. Representative from Mississippi [8]
1995 - Mike Foster, while running for Governor of Louisiana
1995 - Rusty Crowe, Tennessee state senator
1995 - Milton H. Hamilton, Jr, Tennessee state senator
1996 - Ronnie Culbreth, while Georgia State Rep.[9]
1996 - Norm Coleman, while mayor of St. Paul, Minnesota

Lieberman counts, so what do you think? Name names in comments.

I liked this one from the same wikipedia entry:

1991 - Markos Moulitsas, while in the Army

Apologies for publishing too soon. Haven't done this for awhile.