The Intermountain Railway kit is the best, most accurate and most detailed, and it can be built in any stage. At this point, it contains "extra" sections that will never be launched, but it is not missing anything except the European ATV transport module which is not a permanant part of the ISS anyway.
The kit is expensive but worth the price and you can detail it. RealSpaceModels.com sells a detail kit for it and another kit of solary array trusses to enhance it.Try ebay for the kit.
-Ben
www.LaunchPhotography.com