Mostly, the United States. The 1979 Camp David Accords committed America to significant military assistance to Egypt, most recently about $1.3 billion annually. Not all of that is weapons. Still, according to the Stockholm International Peace Research Institute's Arms Transfers Database, in 2009, the U.S. and/or U.S. firms exported about $279 million in arms to Egypt (figure adjusted to 2009 dollars). And, considering arms alone, the United States still supplies the vast majority of military hardware imported by Egypt:
source: NOfP chart via SIPRI data
Question: What happens should that weaponry be used against Israel? Answer: The United Nations will condemn Israel.