I think the main "action" for more SE users to take is just to change their avatar, username, and 'about me' text (that is, if they agree that Monica has been unjustly treated as far as they can tell, given the evidence they can see). Beyond that, there isn't much they can, or should, do against SE.
If you perhaps mean what action we think SE should do, that's easy:
Reinstate Monica.
- Return her diamond on all sites.
- Issue a sincere public apology for the hurt she's been through.
- Issue a statement to the Register clarifying that she is not a bigot.
- If youthey really believe that she needs to be fired for something, put her through a formal process afterwards. Everything will need to be completely transparent, and you'llthey'll have to bend over backwards to show that youthey are being fair and giving her the benefit of the doubt, because otherwise no one will believe the proceedings were anything other than a kangaroo court. But restorereinstate her first.