Blog for Arizona gathers together the media speculation so far:

The Arizona Republic

Republicans

Rep. Jeff Flake

Rep. Trent Franks

Former Rep. John Shadegg

Former Rep. J.D. Hayworth

Former Arizona Attorney General Grant Woods

Former Arizona Treasurer Dean Martin

Pinal County Sheriff Paul Babeu

Former U.S. Transportation Secretary Mary Peters

Mesa Mayor Scott Smith

Democrats

Rep. Gabrielle Giffords

Secretary of Homeland Security Janet Napolitano

Former Arizona Democratic Party Chairman Jim Pederson

Former Arizona Attorney General nominee Felecia Rotellini

U.S. Attorney Dennis Burke

Former Phoenix Mayor Paul Johnson

Phoenix Mayor Phil Gordon

Arizona Board of Regents member Fred DuVal

Arizona Daily Star

Republicans

Rep. Jeff Flake

Rep. Ben Quayle

Former Rep. John Shadegg

Former Rep. J.D. Hayworth

Former Arizona Attorney General Grant Woods

Former Arizona Treasurer Dean Martin

Senate President Russell Pearce

Pinal County Sheriff Paul Babeu

Democrats

Rep. Gabrielle Giffords

Rep. Ed Pastor

Former Rep. Harry Mitchell

Former Rep. Ann Kirkpatrick

Phoenix Mayor Phil Gordon

Secretary of Homeland Security Janet Napolitano

Former Arizona Democratic Party Chairman Jim Pederson

It's a little strange to see people who've lost elections recently in the potential mix like Jim Pederson, but I guess Arizona is the land where no candidate is too improbable.