Dictionary.com Dictionary & Thesaurus - Free Of course there is going to be a time when you need to look up a word, but instead of flipping through a book just pull out this app. The offline capabilities make it a must.
WolframAlpha Just like their website, WolframAlpha can help you with a large amount of questions that may have been bothering you, but in a nicely designed app. Internet required.
iBlueSky (mindmapping) Put away your paper and pen and let iBlueSky do your paper preparations for you. If the $9.99 price tag is too high for you there are many other apps which you can choose instead.
iStudiez Pro There is a plethora of timetable apps out there and I haven't yet had the chance to review them all but this, like many others, is handy to keep track of your day.
Evernote A great way to sync text, photo, and voice notes to both your iDevice and your computer.
Solipskier Not educational but of course everyone needs a break, all work and no play and all that. This game is good because not only is it addictive, you only need one finger to play thus making it a perfect way to subtly waste your time!