Here are some links to refresh your memory:
http://www.bbc.co.uk/bitesize/ks2/maths/number/percentages/play/
http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks2/maths/percentages/index.htm
http://www.topmarks.co.uk/interactive.aspx?cat=24 (Lots of games here, including ratio at the bottom of the list)
Ratio Rumble is a great game - also available free at the Apple App Store!