The Dominoes, Trominoes, and Tetrominoes ClipArt gallery offers 13 illustrations of these geometric shapes that are connected orthogonally, and have 2, 3, and 4 squares, respectively.
One Domino
A One-Sided Tetromino
A poster of five Free Tetrominoes
A poster of seven One-Sided Tetrominoes
A One-Sided Tromino
A poster of both Trominoes