Siding
My personal feeling is there is nothing that blends in more appropriately with the surroundings than clapboard siding. The rear wall's siding was in excellent condition, but the front wall was in terrible condition with several locations where you could easily put your hand into the building. The south wall needed extensive repair and replacement of missing clapboard and the north wall was in slightly better condition.
So we decided that a nice, textured vinyl siding, with a historically traditional school house brick red color, would be a wise substitution. It would also allow us to insulate the interior and put a vapor barrier. And best of all it would not require maintenance - no scraping, caulking and painting every several years (much of it high up on ladders).
Next to the roof, this was the best spent money.