The annual prize honours the UK celebrities with the best bottoms. Previous recipients include Charlotte Church, Will Young, Frank Skinner and Sian Lloyd.
Thomas, who plays builder Jason Grimshaw on Coronation Street, said of the accolade: "It brings a new meaning to the phrase 'builders bum'."
Ellison said: "I am thrilled to be voted Rear Of The Year 2008. My love of dancing throughout my life has obviously contributed to a nicely toned rear."
Award organiser Tony Edwards added: "The annual Rear Of The Year awards have become something of a national institution.
"We believe it is important that this essentially fun event should now continue into the future with strong links to charity awareness."