You're too late for the Sziget festival in Hungary -
Mark's blogging from there these days, (appropriately for you, he seems to be spending a lot of time watching penises flapping in the breeze)
As for Paris, the last big one is
Rock En Seine this weekend (24-26 August) - but there's a smaller Paris festival called
Fete de L'Humanite on 14-16 September: Razorlight, John Butler Trio and Iggy & The Stooges are the only big international names there.
Instead of the capital you should probably go to Marseilles for the
Marsatac festival from 21 to 30 September - a week of all sorts of concerts, including the Divine Comedy, Architecture in Helsinki, Simian Mobile Disco, GusGus, The Dead 60s, Mos Def and loads more...