According to this link (in swedish), Swedish Canon VP Robert Westin says Canon will announce a new DSLR the week of January 24, just before the PMA 08 show, where Canon and all other camera makers announce new products each year.

My money is on a successor to the Canon 5D with a Mark II version, or maybe a Rebel XTi replacement like a 450D or something. They are both at or over the typical 18 month lifespan Canon sticks to.