David Dahlem made two collections, DD1 and DD2. Both published for the first time in 2009 at the Yahoo Sokoban Group, “You Like Sokoban? Interested in Puzzles? Here!”
The puzzles vary from probably autogenerated small difficult levels to big levels with small challenge. You will also get many fibonacci levels and many combinations and minor variations of the levels.
Minglw and York Shen contributed to a few of the puzzles.
Find one of my favorites below, puzzle 26 from DD2:
Among several places you can get Davids levels from LetsLogic.com:
icon-external-link David Dahlem – DD1 (50)(2009)
icon-external-link David Dahlem – DD2 (100)(2009)
The skin is Balls by Hans-Dietrich Pester.