If I could have just one block, it would be Drunkard's Path. It can turn into Wonder of the World, Rocky Road to Dublin, Solomon's Puzzle, Dirty Windows, Fool's Puzzle, Love Ring, Mohawk Trail, and dozens more by simple path rotation and color choices. Here are some from Marti Mitchell.
http://www.frommarti.com/dpgrids.html My avatar also combines Drunkar's Path and strip piecing.