Games - Cubox - Sliding Block Puzzle

I found a new source of online computer games:

http://www.channel4.com/entertainment/games/

One I like in particular is:

http://www.unclebenny.com/nickel/CUBOX/cubox.html

It is sliding block puzzle, and it is a little curious. Most solutions can be done in six moves. Sometimes I can just look at the puzzle and instantly know how to solve it. Others will baffle me for a long time. What is even odder, is that I can come back and replay puzzles I solved easily before, and have a very difficult time solving them the second time. Others that I had difficulty with before, I solve easily.

Update September 2015: Links are not, but they are pretty useless.