OK, I'll play...
Canon EF 17-40mm f/4L. I use this lens a lot, mostly with my 5D Mark II to go ultra-wide, but also with my 7D when I need a weather-sealed normal zoom.
Canon EF 100mm f/2.8L macro. I adore this lens, but I use it a bit less now that I have the 70-200.
Canon EF 70-200mm f/4L IS. A very portable, versatile, and sharp lens that I would never in a million years trade for a behemoth f/2.8 model. This lens goes everywhere with me because it's so compact and relatively light.
Canon TS-E 24mm f3.5L. A specialty lens, so it gets less use than the others.
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Canon EF-S 17-55mm f/2.8. Only works with my APS-C camera, but it's my main workhorse lens on that one.
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Canon EF 50mm f/1.8mm. I can't remember the last time I used it, but it's light as a feather, so it's usually tucked somewhere in my camera bag.