All mods work on a mac--you just have to put the banner graphic and .dm and any folders with graphics into the 'mod' folder(you may have to make one...it goes in the base dom3 folder).
In terms of core gameplay mods,
CBM is pretty much where it's at. A lot of that is because other gameplay mods if they're any good tend to get incorporated into it. I could suggest things like the
Underwater Gameplay Improvement Mod, but most of its changes are already in the latest CBM versions. People sometimes use the
Endgame Diversity Mod by itself.
Over on the SomethingAwful forums a modder called Ninjadebugger has some other core gameplay-ish mods--
AwesomeGods and
AwesomeEndgame, which do pretty much what they say. AwesomeEndgame is basically a more high-powered and further-reaching Endgame Diversity Mod.
As a smaller thing,
Single Age Complete can be useful for, say, a fight between all three eras of Ulms.