This link should be in every puzzler's bookmarks - Angela und Otto Janko
There you will find a large collection of puzzles solvable online using their applets.
eg, for Masyu, there are presently 260 graded puzzles to solve.
They have also kindly offered a link to Google Translate to help with understanding the German instructions.
However, for those puzzles with applets, the applets will only work while the German text is displayed.