Interactive Websites to Engage the Brain

http://staffweb.peoriaud.k12.az.us/Sarah_Bondy/mathwebsites.htm

More K-2 Interactive Smartboard Lessons

http://www.crickweb.co.uk/ks1numeracy.html#start

Enrichment Activities

This is a British site so it is organized in stages rather than grades. 
http://nrich.maths.org/public/monthindex.php?mm=1