are you talking in terms of investments and re-saleability of items, or just to buy stuff to have stuff?
in this day and age, everybody who wants to sell something and every auction house use ebay, yahoo and whatever other online auction site out there to get a feel for fair and balanced market value.
your best bet on getting deals however is to take the drive to middle of no-where auction and the ones that start at like 7am. chances are, less people will be there