I enjoy Sokoban solving. Here is a small collection of levels that I have composed myself.
In related news, I have written an Android app that plays a variant of Sokoban, Multiban.
The following is a SOK (Sokoban Labyrinth) file.
You can copy/paste the contents into the program of your choice that plays SOK files in order to play these levels.
Have the SmartSokoban iOS app? Point it to sokoban://secondepoch.com/sokoban/ses.sok