Question

The International Space Station (ISS) had many of its components launched by the Space Shuttle. After the Space Shuttle's retirement, what is the proposed launch vehicle for new ISS sections?

Answer 1

The only remaining module wasn't specifically built for the shuttle -- Nauka will be going up on a Proton-M.

The issue with extending the shuttle was that there were a number of modules that were specifically sized for the shuttle, and there were some concerns of how it would look to our foreign partners who had built sections like Kibo, Tranquility, Rassvet and Leonardo, if we suddenly took away their only method of getting those modules up there. There was a question of how that would affect NASA's current and future collaboration with other countries.

Not all modules were built to be flown in the Shuttle; although the Shuttle did do the majority of the lifting, there were a half dozen or so that Russians took up.

update : I should've qualified it as 'remaining module after the shuttle is retired', there'd only be one left ... Jeremy is correct in that there's a module scheduled to go up in the last shuttle launch later this month.