Israel gets very little in the form of financial aid from the US what it gets is $2.5 billion in annual military aid and that helps Americans more than Israel. Military aid can only be spent on American weapons so it can't be taken ans used abroad. It giver the US a power of veto over who and what Israel can sell domestically produced weapons to which the US has used in the past to kill competition from Israel and tried to push American equivilents. It also allows America to keep advanced weapons out of the hands of countries it considers potentially hostile like China. It giver the US alot of political muscle over Israel. If Israel buys an F16 with military aid it needs spare parts for that F16 and that sort of thing. If it buys some F16s with military aid if it wants a whole fleet of them it can't all be paid for with military aid. Military aid is basically a buy 2 get 1 free kind of offer because Israel spends more on US weapons each year than it gets in aid.
from the article: Bin Laden: Attacks on U.S. to go on as long as it supports Israel