I recently discovered Soukoban...one of the most simple and intuitive brain teaser/puzzle game but yet quite challenging(esp. levels 10, 11, 12). Currently working my way past Level 34.
You can download a free copy from this link http://hlavolamy.szm.sk/download/iq-tests-logic-games.htm
If you have liked Chip's Challenge or PocoMan, you are bound to enjoy Soukoban.
Beware: It can be highly addictive..Try only if you have spare cycles in your day! :)