And don't buy them when you get the list either. Wait until you have spoken with the second years to see which books are best, which are useless and which are the MS-2's willing to sell you used for cheap. The syllabi at our school typically are so good that we need few textbooks. I use the library copies, the reserve copies, on-line copies (this is becoming more common and something to ask the school if the students have free access on-line book sources...i.e. MD-Consult, Ovid On-line Books, etc) when I really need a particular book. Some of the essential books so far include a good atlas Netter's or possibly Clemente or Grant's; and Robbins Pathologic Basis of Disease (fairly cheap book for the size and content and they're usually available used via bn.com or ebay.com).
Unless you like to collect books (which is not a bad thing at all assuming you have the cash to do so) don't bother buying books early.