Although not cavaquinho related,  it is good to know the theory of chords. I often use the following site:

http://www.harmony-central.com/Guitar/chord-and-theory-chart.txt

There is a nice list of cavaquinho chords online accessible here:

http://cavacoprodgbd.badiuforti.com/

This comes from an iphone application. It does not display some chords though (such as A#)

Sometimes ago I found a simple of all cavaquinho chords that could fit one page. I could not find it again but I did have a print so I did sum-up the content here