Lenses i have experience with
all used in canon mount on 350d, 40d and 1dmk2n bodys
Canon 18-55mm f4-5.6
Cheap "kit lens" it works but it isnt great
only fits 1.6crop cameras (20d,30d,40d,50d 300d,350d,400d,450d,1000d)
Hard to manually focus
canon 75-300mm f4-5.6 (non USM version)
a good light lens, with a fairly long zoom range
Pros - Cheap Long zoom, pretty good quality for the price
Cons - S L O W Autofocus, slow aperture
Canon 50mm f1.8
Small light cheap prime Practically disposable for the price
Pros - great for low light stuff or those on a budget, very sharp (especially for the price) great as a portrait lens
Cons - Very flimsy construction - easy to break, Autofocus accuracy isnt too good in low light, choppy Bokeh, Noisy AF
Sigma 10-20mm f4-5.6
good sharp wide angle
Pros - will fit all canon bodys (including film cameras) focuses fast and accurately
Cons - vignettes at the wide end on full frame and 1.3 crop bodys (all 1d and 5d models, and film camera bodys) has a very distinctive look that some may not like
Sigma 24-70mm f2.8
good cheap f2.8 "walkaround lens"
Pros - well built, fast aperture, 1/3rd the price of the Canon L equivalent
Cons - expensive 86mm filter size, heavy, irritating method of switching between manual and auto focus, Sounds like a swarm of bees when autofocusing
Sigma 70-200mm f2.8
practically lives on my 1dmk2n
Pros - 1/2 the price of the canon L series equivalent, built solidly, focuses fast
Cons - isnt the cool white colour of the canon equvalent
Canon 300mm f2.8 L IS
The lens to own for motorsport
Pros - Lightning quick autofocus, very sharp, Image stabilization works very well, can preset a focus distance and return to it quickly by turning a ring, takes a teleconverter very well, hand holdable for short periods of time, Very nice Creamy Bokeh
Cons - Very expensive (7-10k), heavy (4kg), can damage lens mounts/mirror boxes if you pick it up by the camera body instead of the lens.
Canon 400mm f2.8L IS
As above - just longer and heavier
dont even think about trying to hand hold this one - 7ish kilos, and 10-15grand
need a monopod or tripod, and some experience in using long lenses/heavy lenses, but if you have the technique the image quality is brilliant