filter bittorent and so on

Hi,

I know it's not the real usage of netfilter/iptables, but I am looking for something in order to filter (block) all traffic related to some usage of the network. Especially, I target those using much bandwidth (P2P, VoiIP/Skype,...)
Those things can be encapsulated into some other protocol or be used through some authurized ports (such as 80).
What would you recommend in order to filter that out?

Thank you.

                             Chef de projet chez Vectoris
                                 Phone: +261 33 11 207 36
System: xUbuntu 8.10 with almost all from package install
   http://www.google.com/search?q=mihamina+rakotomandimby

http://l7-filter.sourceforge.net/protocols.en.php?sort=quality
seems to be one solution, without filtering but just with load balancing.

                             Chef de projet chez Vectoris
                                 Phone: +261 33 11 207 36
System: xUbuntu 8.10 with almost all from package install
   http://www.google.com/search?q=mihamina+rakotomandimby