Test your number sense with these tools, and improve it with these games:
(1) Johns Hopkins University: Test of Number Sense (Flash required)
Articles: NYT (2008) Gut Instinct's Surprising Role in Math
NATURE (10/2/08). Individual differences in non-verbal number acuity
Meet the Number Sense researchers at Johns Hopkins University
(2) Panamath. Test of Number Sense
Podcast: NATURE magazine Podcast with Justin Halberda (Sept, 11, 2008)
(3) Number Sense
Articles: Scientific American (1/9/13). Numbers Games Devised to Aid People with "Dyscalculia"
THE NEW YORKER (3/3/08). Numbers Guy. Are our brains wired for math?
Discover Magazine (July/Aug. 2013). How can a smart kid be so bad at math?
Smithsonian Magazine (1/11/13) Dyscalculia, Like Dyslexia for Numbers,
(4) Developing Number Sense: http://low-numeracy.ning.com/. Games that help.