Best songwriters

[Led Zeppelin]

I reckon

Bob Dylan
Don McLean
John Lennon (Beatles)
Noel Gallagher (Oasis)
Eric Clapton
Axl Rose/Izzy Stradlin (Guns N Roses)

[zepp_rules]

Bob Dylan
Jimmy Page & Robert Plant
Lennon & Mcartney
Izzy Stradlin
Eric Clapton
Jimi Hendrix

[stratman42]

Neil Young
Kurt Cobain

and others

[Raskolnikov]

Mark Sandman
Robert and Dean DeLeo
Les Claypool
Selene Vigil and Elizabeth Davis
Jerry Cantrell

[stratman42]

Roger Waters
Neil Peart
Izzy Stradlin
Hendrix

[Bardsley]

Dylan (Need I say more?)
Lennon & McCartney
Neil Finn
Neil Young
Hendrix

[NIck Lowe]

I don't think you have to look much further than Toby Jepson of the now defunct Little Angels to find one of the best most underrated British songwriters ever.
For content and lyrical style he wrote some of the cleverest and thoughtful songs I've ever heard. I don't know why the band finished because they could and probably should have been one of the biggest bands in the world. Oh well, c'est la vie.
Top Amrican songwriter, well I don't know but Bruce Springsteen has to be up there, especially the earlier stuff.

[Locrian]

HENDRIX!!!
come on! to write that much quality music in such a short amount of time is amazing! His songs are so damn catchy.