Citeseer, Google Scholar, etc. Finding related research is a huge part of grad school.
A program to help you organize references. All the related work and papers you've read/cited. I used a spreadsheet and the Mac-based Papers. When it comes time to write chapter 2 of your thesis ("Related Work"), the work you did five years ago will be fuzzy; writing it down is essential.
A good bibliography tool. If you're using LaTeX, BibTeX is okay, but a tool like the above that can autogenerate the TeX is even better. As you craft papers for different conferences/journals, it can be overwhelming to find that one reference you really need. Tagging and categorizing things up front is helpful.
Presentation skills. If you cannot clearly and concisely explain your ideas, you will have a very hard time defending your thesis or presenting at conferences. Practice in front of the mirror, your mom, your gaming guild, whoever you can get to sit still for a minute.
Presentation software. Whatever you like. Keynote was great for me; PPT is of course the standard. Even the Google Docs equivalent. Learn to be concise and informative.
PhD Comics. Because it is way too accurate.
And, of course, the local free-food list. ;)