Keynote wins for best presentation software hands down -- but you already have PowerPoint. I use OmniFocus and iCal to keep things organized, and use my iPod Touch as a PDA. You'll want to have both Safari and Firefox, as some university resources have intermittent issues with Safari (e.g. ANGEL, Blackboard, etc.). You may also, eventually, need software that is more specific to your major. If you use a lot of pdfs, for articles and other course material, you may want to invest in DevonThink. I use this everyday, but I handle thousands of articles in pdf format. You can also use it to organize notes, if you take them on your laptop.
That's what comes to mind now. Check out your university's computer store and see what prices they offer. My current university offers discounts that are better than one can get online (I bought Office 2008 for $60).
Hope this helps...