I agree, the 3M stuff is great and should sell for about $1/ft in your local bike shop or hardware store. If you want more colors and choices than standard red, amber and white, here's some links to Identi-tape's web site:

http://www.identi-tape.com/hi-intensity.htm
http://www.identi-tape.com/safetyonetwo.htm


I've bought from them before online - both their product and service is excellent! They've also got other product like sew-on and iron-on reflective fabric strips, etc., see their index at:

http://www.identi-tape.com/index.html