The one-time pad has been proven to be uncrackable. It requires you to exchange a 'pad' of data with the person you want to communicate with, and the 'pad' is also consumable.
For example, you could give a friend a 1 gig memory stick with a pad on it and they would do the same the same. You could then each transmit 1 gig of data encrypted before the pad was used up, and be 100% certain that the data couldn't be decrypted. This assumes that your pads are totally random, which can be a tricky thing to achieve.
There is some talk about fractal encryption being quantum resistant, but it would still theoretically be crackable I think, just very difficult.