The process of getting a visa to Jordan for different nationalities is a bit complex to explain. The following is attempting to explain some of the side of the procedures for different nationalities as experienced by Safarists.
No visa needed. (See LADIES section below)
BY CAR (Ferry at Aqaba):
You MUST be hosted by a Travel Agent (they provide hotel residence or other papers), or show a valid "Work Contract" in Jordan for every traveler (everybody in the Car, if you're bringing it up). Without those documents, you'll be turned back!
JORDANIAN EMBASSY IN CAIRO:
The official standing from embassy insists that Egyptians are not asked anything on crossing from any border points to Jordan and don't advice you on the above through any official way. The reason for this maybe that they don't wish to have a confrontation with the Egyptian Government on (mo3amalah be elmesl) which means that Jordanians will not be allowed in easily as they're now. It's thought that both Governments are trying to handle the issue of illegal Egyptian workers in Jordan in the lowest-profile possible and that that is the reason for this status.
Egyptian ladies in any land border points may be asked by the Egyptian Government to show permission (taken from elMogamma3) if they're not accompanied by their husbands. This seems to be based on the judgment of the Border Officer (whether to ask for those papers or not). It has been said informally that this is to control/reduce the outflow of illegal prostitution from Egypt, but is practiced by the authorities in a discreet way. The permission they're asking for is --mostly-- that the Lady is a university graduate. It has been said --officially-- that Gentlemen need that as well but according to all reports this seems to be unnecessary. It's also unnecessary for Ladies traveling with their husbands or in most well-identified groups.
Visa granted in airports and in Aqaba automatically.