solve

 https://www.google.com/search?q=puzzle+solve

size

 https://www.google.com/search?q=puzzle+size

giant

 https://www.google.com/search?q=giant+puzzle

Mind

https://www.google.com/search?q=mind+reasoning

Concept

https://www.conceptispuzzles.com/ 

Sudoku / Learn / Tutorial

https://www.google.com/search?q=sudko&oq=sudko

http://www.youtube.com/user/learntoplaysudoku/videos?flow=grid&view=0
http://www.youtube.com/user/dkmpuzzles/videos?flow=grid&view=0

Line

Royal

jig

Riddles with Answers

http://en.wikipedia.org/wiki/Riddle

Site
http://www.riddles.com/

Just
http://www.justriddlesandmore.com/

Brain
https://riddlesbrainteasers.com/

Good
http://goodriddlesnow.com/

Buzzle
http://www.buzzle.com/articles/riddles/

Directory
http://www.dmoz.org/Games/Puzzles/Brain_Teasers/Riddles/

Tube
https://www.youtube.com/results?search_query=Riddle+questions

Slides
http://www.slideshare.net/search/slideshow?searchfrom=header&q=Riddle