Quote for my iPod

I noticed I finally have the money - and the regular moneyflow to ensure I wont regret my decision - of buying an iPod. The cheapest way of buying it is from Apple's netstore (shipping is free). They also offer to engrave the 'pod for me, for free.

I want something nifty to that space. Maybe mathematical function, or quote from some famous thinker (but not one so common that Everyman knows it - I want to be pretentious) or from a famous book. It should fit to my personality. By know, you should know what it is.

Im really looking for a quote that has reference material. Like, where is it from, when it was written?

And last, it should be on two lines (max), with both lines 27 characters or under. Any suggestions?