Canon is pulling out the stops prior to the CP+ Camera and Photo Imaging show in Yokohama, Japan which is taking place on February 9th, 10th 11th and 12th (2011).
Today they announced two new super telephoto lenses, the Canon EF 500/4L IS USM II and the Canon EF 600/4L IS USM II which will be available later this year. That's the good news. Now for the bad news. The expected retail price of the EF 500/4L IS II USM is $9499 and the expected retail price of the EF 600/4L IS II USM is $11,999. Note that Canon suggest these will be the retail prices, not the "list" prices, so they represent what you will actually have to pay to get one! If your wallet is deep enough you should be able to get your hands on the 500mm in May, but you'll have to wait until June for the 600mm. These two lenses complete the "II" series telphoto lineup, with the EF 300/2.8L IS II USM and EF 400/2.8L IS II USM which were announced last August (2010).
Improvements to the current 500/4L IS and 600/4L IS lenses include lower weight through the use of magnesium alloys, a new optical design which includes a second Fluorite element, an improved IS system giving up to 4 stops of stabilization and improved anti-reflection coatings on the lens elements.
In another announcement, Canon revealed details of a new Canon EF 200-400/4L IS USM lens which is in development. The unique feature of this lens is that it will have a 1.4x extender built into it which can be moved into the optical path to give a 280-560/5.6 lens. Though they don't comment on why they are using the built in extender, I can think of two reasons. First it will be much faster and more convenient to flip a lever then it is to remove a lens, add an extender and remount the lens. Second, the optics of the extender can be designed to properly match the optics of the lens. No compromises will be needed as may be the case in an extender which has to work with a whole range of lenses. No word on availability or price, but I suspect the price won't be a pleasant surprise. I wouldn't be stunned if it was up there with the 500/4L IS II USM close to the $10,000 mark. The Nikon 200-400/4 ED VR II (no built in extender) currently sells for $6,800, so it's very likely to be more than that.
Here are all the details from Canon: