I highly recommend Markus Hutter's book: "Universal Artificial Intelligence: Sequential Decisions Based On Algorithmic Probability" (http://www.amazon.com/Universal-Artificial-Intelligence-Algo... )

Beware, you need some serious maths and a board to follow him. In the end the book is quite rewarding.

Now to AIXI: I don't belive that having a formula solves AI problem. Yes you can model it, but in real environment, I believe there are simpler models to try first. Remember: nature like simpliness first, complex when needed.