Canon EF 24-70mm f/2.8L IS USM Lens
Take the current Canon EF 24-70mm f/2.8L USM Lens and add a 4-stop image stabilizer. Of course I'll take any optical improvements possible as well. In addition to giving us an awesome lens, Canon would give those of us trying to decide between and help others decide between the 24-70 L and 24-105 L huge time savings. I asked for this lens a long time ago - and will keep asking until I get it or something better. :)
Canon EF 16-50mm f/5.6L IS USM Lens
Landscape photography is extremely popular - how about a landscape-specific lens? Landscape photography often requires deep depth of field - which often translates to narrow apertures and wide angles of view. I'll give up the wide apertures (if I need to) for lighter weight and any other benefits I can have in place of them. IS will let me shoot handheld in many situations - even in strong winds with a circular polarizer in place. I of course need razor sharp images right into the full frame sensor corners, no distortion, no flare, no CA and no vignetting (even with a standard CP filter installed).
Canon EF 500mm f/5.6L IS USM Lens
I would like to see a great bird and wildlife photography lens that is both smaller and much more affordable than the current supertelephoto lenses but am not willing to accept less than perfection in the image quality attributes. The gap between the 400mm f/5.6L lenses and the big guns leaves a gap for such a lens. Make it 5/8 the dimensions of the 800 f/5.6 and 1/8 the cost. I know - I'm dreaming about that last part.
Canon EOS-1Ds IV Digital SLR
Based on the past EOS 1Ds release schedule, the 1Ds IV is now overdue. While the current 1Ds III remains my favorite camera, I am ready for the latest DSLR features (horizon level, better LCD, HD video ...) to be added to it. Increase the resolution and frame rate too.
Canon Digital Photo Professional (DPP) Improvements
DPP makes getting great image quality easy, but this application could be so much better. With so many million Canon EOS DSLRs in circulation, improving DPP would benefit a huge customer base - which can only be a good thing for Canon.
New Canon Lens Cap Design
How hard would it be to give us a center- AND side-pinch Canon lens cap like all of the other lens manufacturers? Better yet, leap frog this design with something even better. Just make sure the lenses sit flat when placed on their installed lens cap.
Canon Lens Hoods for All
I want the proper lens hood to come with all Canon lenses I purchase - not just L lenses.
Increased Canon Lens Warranty Period
Canon USA's 1 yr lens warranty appears stingy next to those of Sigma USA and Tamron USA. Canon makes great quality gear - the warranty should reflect this. Most repairs are needed early in the life of a product anyway.