Physics for Scientists and Engineers, sixth ed. by Tipler and Mosca, volumes 1, 2 & 3 (2 and 3 are in one book)
Both of these text books are necessary for the Physics 12x series. My copies of the books are special, in that they are loose leaf. Yes, you need a binder to put the pages in, but since they are loose leaf you can carry around only the necessary chapters, rather than the entire text book! Imagine being able to carry your text book with you, but barely adding any weight to your backpack. The loose leaf version of the Tipler text books is not available for sale anywhere -- I got it at my college last year (I transfered) as a special deal to that school only -- but we weren't able to sell the books back. There is minor hilighting in perhaps half of the chapters, the pages are in good condition.
Biological Science, third ed. by Scott Freeman, including CD
This book is necessary for ESRM/FISH 162, BIO 180, 200, 220. My copy is perfectly new -- I bet the binding will creak when you open it. There is no hilighting, no smudges, crinkled pages, or dented corners. Perfectly new. I even have the acompanying CD -- you can't get the CD from the bookstore if you buy a used book.
Elementary Differential Equations and Boundary Value Problems Student Solutions Manual, eighth ed. by Boyce and DiPrima
This book is very useful for MATH 307, I used it often. It is in almost new condition, with no hilighting, smudges or ripped pages. (I'm very good to my books.)
Sociology of the Family, Sociology 352, a custom text for the UW, by Pepper Schwartz
This is for (if you haven't guessed it) Soc 352, but is only useful if the class is taught by Pepper Schwartz. It has hilighting all throughout, and a slightly used-looking binding.
Tutorials in Introductory Physics workbooks by McDermott and Shaffer
I mentioned above that I was a transfer -- I had to buy these workbooks, and then only used the last third of them, if that. The TAs often photocopied homework to give us instead. I heard that there are science students who only need to take the first two physics courses: 121 and 122 (I think engineering?). These books would be perfect for them. They are in good condition, some writing in the workbook and some missing pages in the homework book (what we had to tear out and hand in) but overall really good condition. Or, if you're going to take the PHYS 12x series and don't mind photocopying some of the homework pages from the 123 class, you're going to get a good book from me for a lot cheaper than the bookstore.
Markets and the Environment by Keohane and Olmstead
This is for ENVIR/ECON/ESS 235 -- Evironmental Economics. I do not know if this is the first or only year for this book, so unlike the bio, math, and phys books, you should make sure you need it before buying. It is in really good condition, with sporadic hilighting.