For the summer block, I suggest buying Epidemiology by Leon Gordis and reading it cover to cover. That's a really good book, and epi is a subject that is tested on the boards. I didn't like the stats book they assigned us, and I wound up getting a better book from the TA. I did buy the JMP Manual book, and that was useful for learning stats as well as for learning how to perform various statistical tests for the stats projects we had to do. So for the summer block, those are the only two books that I would recommend buying.
There really aren't too many new books that you need for second year beyond Robbins and Cotran Pathologic Basis of Disease, which is why I haven't been writing posts about second year books. Some of my classmates felt that Robbins was too dense, but I thought it was really good. I'm not going to get to a few of the chapters at the end like the eye chapter, but I've almost read the whole book cover to cover now. There is an atlas that goes along with the Robbins book that is really good. A lot of us bought it. You can also get the Robbins Review of Pathology, which is a path question book. I liked that book as well, although I think the questions in there are a lot easier than the practice Step 1 questions I've been doing. All of the other books we've used this year are the same as the ones we used last year: Katzung for pharm, Drake's book and modules for anatomy/embryo, etc. The only other books you will need are whatever you plan to use to study for Step 1. But you really can get away without buying too many Step 1 review books, because there is a whole collection of them in the library that you can use. They pretty much have all of the popular review books on reserve.