I know that there is a 20% early withdrawal penalty. But what other taxes will I have to pay on a 90k withdrawal?

Actually, the Early Withdrawal Penalty is 10%.

The 20% figure is what the 401K custodian is required by law to withhold, but that is only a down payment on the amounts of taxes you will actually owe to both the IRS and the state.

The actual amount of tax due depends on your overall annual income for 2009 plus in which state you live.

It will be at least 25%, and may be as high as 50%.