This summer Canon is rumored to announce a new EF 70-300 f/4-5.6 IS full frame lens that will replace the current 70-300 model. The official announcement is expected before August.
Interestingly enough, Nikon is also rumored to announce a new Nikkor 70-300mm f/4.5-5.6 VRII lens before Photokina.
Via CanonRumors