I just recorded an interview with The Trail Show podcast talking about traversing Iceland. In case anyone hears the show and wants more information, I thought I'd organize links.
The standard North-to-South route is described by Jonathan Ley on his webpage. I can't find a GPS track of his route, so please let me know if you know of one. There is a track from FKT, and one from Katie-Jane L’Herpiniere but they both follow the F26 road across the middle of the country, which I would recommend against.
My report describing resupply, lessons learned, and route information, is here. My description of hiking around Hornstrandir in the Westfjords region is here. You can also use the calendar function for July 2014 on the right side of this page to read the short entries I posted while hiking.
Others who have traversed Iceland: Jozef Ivanecky in 2005. Will Copestake writing for Sidetracked. Łukasz Supergan did it east-west, and again in winter. Andrew Skurka/ did it east-west as well, and has useful general planning information. Folks mountain biked across the country and wrote about it for the Strava blog.