Websites

Lateral Puzzles a forum where like minded souls can publish their own puzzles, and participate as people attempt to solve them.

Michael Kelly's Page of Misery is a new and unusual take on some common lateral thinking puzzles.

Books

Test Your Creative Thinking by Lloyd King

Working things out that is. I found Lloyds puzzle books to be incredibly entertaining and really helped me think outside the box. This is actually not an unheard of phenomena and is supported by many researchers in the field of creativity, that one can improve ones capacity for creative thought with puzzles like these. I found this book to be a lot of fun and would strongly reccomend it.