Rainbows 
http://hanksville.phast.umass.edu/defs/rainbow.html 
Single page with good explanation. Only one diagram but still a good overview for anyone just wanting to get the gist of how rainbows come to be. 

Questions About Rainbows 
http://www.deltatech.com/rainbowx.html 
This page includes lots of interesting facts and answers to frequently asked questions - worth a look. 

Rainbow 
http://science.kongju.ac.kr/phys/shin/experiment/ntnujava/Rainbow/rainbow.html 
This site is fantastic. It has a diagram of the rays of light entering a raindrop that allows you to change the colour of the light and the incident angle to see what happens and an in-depth description of the physics involved for anyone who wants more detail than that provided here. The parent site, The Virtual Physics Lab is probably worth bookmarking for its value in this and other area of physics. 

Circles of Light - The mathematics of rainbows. 
http://www.geom.umn.edu/education/calc-init/rainbow/ 
This site includes experiments for investigation of rainbows and questions to guide students to a very good understanding. Some of the information may be a bit beyond the average year 11 student but still well worth a look - especially for help with work requirements such as the practical investigations. 

Rainbows 
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/wtr/rnbw/frm.rxml 
This site has some really great diagrams and photos. Some iof the best pics of secondary rainbows on the web. Good explanations too. Check this one out! 

Rainbow Photographs
http://atmos.es.mq.edu.au/AMOS/weatherwatch/rainbows.htm
This site has lots of photos of rainbows in New South Wales. Worth a look but read the copyright notice if you want to use any of the images.