I agree with most of the statements here, each lens certainly could have a completely different use for every person. That being said I'll list and tell for me, but it's only me, and YMMV.
Canon 8-15 fisheye. Specialty, effects lens. Ultra wide angle with tons of distortion. I Like the effect, I'm still trying to learn how to use it. Especially trying to figure out how to stay out of the frame myself, whether it's my shadow, or my feet.
Canon 17-40 f/4 UWA on my FF body now, WA on my Crop. This was my first lens purchase after digital with my crop body, and it remains in my bag. I will use this lens for just about anything that needs a wide shot. For my style that's not too often.
Canon 24-105 f/4 IS. Probably the lens that's on either of my bodies the most. WA to normal to short tele depending on the body. Great for walk around, great for everything short. If I'm going to take one lens, this is the one.
Canon 28-70 f/2.8. Oldie but goodie. I've coveted this lens since my film days and finally picked one up a couple of years ago. This is probably my second most used lens. I am debate wether this or the 24-105 stays. It may end up being both, even though they are pretty redundant. Same usage as the 24-105, just about everything. I've been putting this lens on more and more often lately, I miss the 70-105 part sometimes. but appreciate the speed.
Canon 70-200 f/2.8L IS II. What can I really say here. Probably one of the best, if not the best short tele lenses made. This one replaced my much loved first L lens: the 80-200 f/2.8L drainpipe. It surpasses the old drainpipe in every way, but the drainpipe still had something about it. I use this for everything from landscape to portrait to close in sports. Great lens.
Canon 100-400 f/3.5-5.6L IS. This is a compromise lens. I had a 300 f/4L/1.4x Kenco TC, and got frustrated in fast action with changing distances. The ability to zoom with this lens makes it way more versatile than primes. Sports (in good light), critters, landscape, portraits. Good lens, versatile lens.
Canon 500 f/4.5L. Another oldie but goodie. Super Tele. Critters, landscape. Great lens, not versatile, but when you need 500mm...
Sigma 50 f/1.4. I just like this lens better than the Canon lens. When I need speed and a normal focal length, this is the one.
Canon 45 f/2.8. Brand new to me. Specialty lens. I plan to use to correct for building tilt, and to increase DOF for landscapes. I also plan to play with the miniature effect for fun. Basically a normal lens with a lot of specialty adjustments.
Rule books are paper they will not cushion a sudden meeting of stone and metal -ekg-