I'll make it easy for myself, and just give you the URL to a couple of good sites.
Wikipedia gives a good introduction : http://en.wikipedia.org/wiki/Bracteate
Still Wikipedia - under "Further reading", there's "Die Goldbrakteaten der Völkerwanderungszeit. Ikonographischer Katalog." There are detailed descriptions of them in German, but if you just want to see pictures of them you open "Band 1:3", "Band 2:2" and "Band 3:2". If you don't want to study the files online, you'll find a pdf-download pretty high up to the left.
I also gave the bracteates on my site a page of their own :
I'll add more links later on, when I find them....