Why do you want an L lens? What are you hoping that it will do for you as opposed to a non-L lens (either from Canon or other manufacturers)?
I personally use a number of lens and only one of them is a Canon lens. When I needed a faster longer lens (70-200 range) I checked out different reviews and then tested the two that were at the top of the comparisons (Canon 70-200 2.8 and Sigma 70-200 2.8) and found that they compared almost identically in tests and it actual use seemed to give identical results. At the time the Canon lens was about $1100 and the Sigma $700. I bought the Sigma. It has always given great results.
My other workhorse lens, especially for glamour is the Sigma 18-125 f3.5-f6.3 which works like a champ and always gives excellent results.
I use both of these on a Canon 20D. My one Canon lens is a 100mm f2.8 macro lens. Again, in different reviews I compared it against Sigma and Tamron but found that the Canon lens seemed to give substantially different and better results, so I went with it.
Anyway, you should always consider lens purchases based on what you need the lens for and what you hope it will do for you. If you just want an L lens because it looks cool, or for prestige value, then that would not be a really good reason.
Re: Looking For Information On A Lense
Shot with Canon 20D and Sigma 18-125 lens and Novatron power pack flash