US Laptop Data dongles/USB sticks

[viji]

I am going to the US for three weeks, and traveling around a large part of the South West in July/August. Where would I find a data plan for my iPhone that I can share with my laptop via tethering, or a USB data dongle that I can plugin and create whats known as an 'ad-hoc' network? I don't mind paying slightly thru the nose for 2-3GB at the most. Better than £6/mb on 02!