Feel free to add reviews of your lenses to this thread. May help with a lot of lens questions.
My Lenses, used with Canon dSLR
Sigma 12-24mm F/4.5-5.6 EX DG Aspherical
The widest zoom available for full frame. Just been replaced by a Mk2.
IQ is very good, distortion is surprisingly minimal. Focus speed is good. Very good ultrawide zoom at a reasonable price.
Sigma 20mm F1.8 EX Aspherical DG DF RF
Fun, fast prime that has excellent IQ.
Canon EF 24-70mm F2.8 L USM - My favourite lens coupled with the 5D
This is my walkaround/outdoors/landscape lens of choice on my 5D. Great zoom range, big aperture when needed and awesome image quality. Built like a brick too. Superb!
Canon EF 50mm F1.4 USM
A good focal length with a big aperture at a bargain price. Image quality is excellent with good background separation at larger apertures. I rarely use this lens but when I do the results make me glad I own it.
Canon EF 70-200mm F4L IS USM
This is a great lens. Very handy zoom range, very good IS and super sharp pictures. Not too heavy or too big for travel. Only downside may be that its neither a wide nor a long zoom lens. If you need a lens to cover this midrange then the 70-200F4L IS is fantastic.
Sigma 150-500mm f/5-6.3 DG OS HSM APO
Used for general outdoors/offroad shots. Almost permanently attached to my 1D. OS is brilliant and allows me to comfortably shoot handheld. IQ and focus speed are good but since shown up by the 300L. Great bang for the buck!
Cons: Almost unusable in low light.
Canon EF 300mm F4L IS - Second favourite lens coupled with the 7D
I got this lens as I was finding that the 70-200F4L IS was a bit short for some shots and the Sigma 150-500 was too slow for some shots. Combined with the 1.6 crop factor of the 7D this is a really nice tele lens. Sharpness is a given but what I really love is how fast it focuses and holds focus with the 7Ds' extra AF points. A killer combo.
Pros: Superior build quality, Super-sharp images, Fast auto-focus
Sigma 150mm F2.8 EX APO Macro DG HSM
I dont shoot a lot of macro but this lens is very very good. Super sharp and with excellent IQ.
Canon 1.4x extender
Great match for both the 70-200 and the 300. No visible loss of IQ. Drops lens back to max F5.6. Expensive but the results far outweigh the price tag.
Kenko 2x extender
Have only used this for moon shots with the 150-500 and 7D - giving an effective length of 1600mm. 8) No apparent loss of IQ but AF is no longer functioning with any lens slower than F2.8. Not a problem at this length as MF is a must.