If you are interested in "Pic-a-Pix", "Link-a-Pix", "Fill-a-Pix", "Maze-a-Pix" or "Dot-a-Pix" kind of puzzles, this Conceptis Puzzles is best for you. Sometime back conceptispuzzles.com also was one of the sponsors of the World Puzzle Championship. At this site I liked the Pictures made out of puzzles. They are very specialized in making puzzles out of pictures.
Beside from picture puzzles one can also find Sudoku, Kakuro, Hitori, Battleship, Bridges (Hashi), Slitherlinks and now Calcudoku also on this site.