The proof of the four color theorem, the proof of the nonexistence of a projective plane of order 10, the proof of the Kepler conjecture, the search for Mersenne primes, the discovery of the Lorenz attractor and the Feigenbaum constant among others are examples. These are in the wikipedia article on experimental mathematics with other examples. There is also a jounaljournal of experimental mathematics. Also there are some videos here from June and July of 2008 about experimental mathematics. Many of them are about the Landen transformation.
Post Made Community Wiki