Thanks for your advices !
I live in Canada so no amazon.com for me :(
And amazon.ca does not have as much stuff than amazon.com.
So I think I it will be Google :)
And finally, I really think I will go with the AKG K550.
I know a place who sell them at 299$, but I think I can make drop the price a little bit.
Maybe someone could try to make me change my mind one more time ? ;)