More back-to-school suggestions; this one has the advantage of being free. If you haven't already downloaded Firefox for your machine, it's a good idea to have it handy for those occasional sites that aren't Safari-friendly. If you're interested in a few extra plugins with a student-friendly bent, then you might check out the Firefox Campus Edition, which is simply the current Firefox build plus the FoxyTunes, StumbleUpon and Zotero plugins in one convenient package.
FoxyTunes (for controlling your music player via the browser) and StumbleUpon (social bookmarking for interesting/useful sites) are both fine, but the real power tool here is Zotero: this research tool, file manager, PDF bucket and citation editor is a boon to anyone working on research projects with Firefox. Given enough practice with Zotero, it might replace a local note manager like Yojimbo or other online tools like Google Notebook.
Of course, if you already have Firefox, you can download these plugins (or scores of others) separately, and all three are free.