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.
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!