Daily Chess Puzzle
The Chess Tempo web site provides some excellent training problems. One puzzle per day from that site will be displayed here.
The problems are not the typical "mate in X moves". Instead you are shown a position where a key move or sequence of moves will lead to a decisive advantage. The side nearest to you has the move and you move the piece by dragging it with the mouse. Set the problem difficulty level using the buttons at the bottom before being tempted to solve the easy one.