Land Value Tax
According to a study cited by Richard Florida, urban land is worth $25 trillion as of 2010, so a 1% tax, say, would yield $250 billion. Let's say we budget $100 billion less, so that homeowners below a certain income aren't taxed with property tax and a land value tax. Then we would have $150 billion per year from a land value tax.
Some good recent articles on a land value tax:
In praise of a land value tax
How Much Money Could a Land Value Tax Raise?
Land value tax, explained