I suggest buying a Sunday newspaper. The major big box retailers generally have multipage fliers inserted in Sunday papers, and these always feature a selection of name-brand laptops at special prices.
But the special prices usually involve mail-in rebates and I don't know how you could handle this since the rebate is in the form of a cheque mailed to your home, and you won't have a home address in the USA I would suspect.
The big box stores that carry laptops are:
Best Buy and Circuit City (as Richard suggested)
CompUSA (I find they have the best selection of add-ons in my area). Look on the bottom shelves for their cheaper house-brand items.
.. and the major office supply big box stores -
Office Depot (headquarters are in Florida)
Office Max
Staples
Most cities only have two of the three "office" store chains.
seacue