I hope to gradually update this list over time.
In the meantime, the best resource for unpacking abbreviations that I have found is Duden.
Some of the most important abbreviations are explained here.
One helpful tip on abbreviations that I have just been given (by Christoph Markschies) is that there is a convention of signalizing the plural of an abbreviated word by doubling the last letter: “proff.” = professores).
ebd. = ebenda = ibidem = in the same place = as just cited above
Hss. = Handschriften
o. J. = ohne Jahr = without year [hopefully]
m.E. = meines Erachtens = in my view/opinion
u.a. = und and[e]re, und and[e]res, unter ander[e]m, unter ander[e]n = and others OR among other things (inter alia)
u.ö = und öfters = not sure: I think it might have the force of “and often” but it might have the weaker sense of “and occasionally” or “and once in a while” – hence I usually waffle and translate it as “and elsewhere”.