I notice a lot of Wide Aperture Worship in this thread.
I don't really dream of lenses that are very big and heavy.
1. I would love one of those Canon tilt-shift lenses, I have never had such a thing and the possibilities are exciting.
2. The new EF 28mm f2.8 IS is a dream standard lens for me on my 28mm sensor camera. But I will probably never get it because the practical guy inside me keeps saying "your 17-55 includes 28mm, includes f2.8, and includes IS, so what are you thinking!?!"
3. The EF 70-300mm L IS, I dream of this one A LOT because it is probably my next lens purchase!