Conceptis Puzzles is a publisher of nonograms and what they call "link-a-pix" puzzles. On OSes that will run their applet, you can solve 6 new puzzles each week. Many more are available in PDF form (print out and solve), and one weekly one they want your review comments for--they give a t-shirt for one user review each week.
For the weekly puzzles, registration is required but free.
Don't say I didn't warn you!