Andrew hiked the Traverse East-West. His site gives a moderately detailed description of his route, has some handy tips and info, provides a gear list, links to maps, and lists some other useful resources. Caution: His E-W route is rather challenging. You come across a number of glaciers and have to ford many rivers. Probably not the best route for a solo hike; fairly dangerous at parts.
Jonathan and his friend Dave hiked North-South. He provides a quite detailed description of his route and provides some very interesting tips. He invites you to get in touch with him. His route is ultimately shorter and less rugged, but safer from what I can tell. Sticks more to tracks and F-roads where available. Most challenging obstacle appears to be traversing the lava flows (interesting!).
Klara took a rather winding route through different parts of the island. Her post is not the most useful for planning your own trip, but her video is stunning and really puts the fire in your heart to get out there and do it!
Book about a man’s journey across Iceland. Might be a bit outdated. I have yet to read it but I’ve heard it’s quite useful.
Broken English but some references to maps and direction.