I found this site, called German Dialects on the Internet (look at the EDIT part below), which is supposed to help teachers, both from High Schools and Universities to help their students to better understand the dialectal differences among the various German regions and the other German-speaking countries.
I've tried some links, and unfortunately not all seem to work directly clicking from there, but I searched them and listed the working ones and the other ones in the edit below.
Since some were commenting that the links don't work, I'll directly link them here, signalling the ones I found by myself, if you find the missing ones, feel free to add the link:
You can also go to this page, where you'll find a map and a short cataloguing of the main dialects. If you scroll down, there is a link to Dictionary resources, which is not a classic dictionary but better a collection of expressions in German and other dialects ordered by topic; you can find it here.
Hope it was helpful!