A good advice I've read and heard many times:
If you don't know why you're getting it, you don't need it.
Get to know the gear you got first and then judge if you need more or better lenses. Or if you got just shitload of money to spend (I'm talking about the "wiping your ass with $100 bills" level) then just go all out with any and every L lens you see (note that this last sentece is really
bad advice).
I don't know whether you're total beginner or full pro (not very likely?
) or whatever but sounds like you need to do more research on lenses overall and get to know what means what and how stuff work. You can always get more and better gear later but what's the point if you don't really need them or don't know how to get the best out of them. I know I'm lusting after all them red circle (Canon L series) lenses when I see them but I know I don't really need them since I'm just a hobbyist. Nor can I even afford them. >.<