I am an Australian resident on an E3 visa and I have just completed a 3 month contract in the USA. My total earnings will be in the vicinity of $3,000.
Could you tell me if I will need to pay tax on this?

E3 is work visa. If your total earning is around $3,000 then you do not pay any federal income tax. If income tax is withheld, then you will file nonresident tax return and get the refund. Your personal exemption in 2009 is $3,650.