The main reason for LHC is to prove the existence of the Higgs particle, I guess.
Then there is also the possibility of finding some more hint that what we do in String theory. Answers to questions like "Are there supersymmetric 'mirror' particles?" and "Does black holes leak gravity into other dimensions?".

Since some of you gave some links to enlighten people of the subject, I'll do the same. Recently I wrote a small paper about supersymmetry, if you are interested to get introduces to the subject: http://www.isv.uu.se/~rathsman/group...ack-report.pdf
(some quantum mechanics and/or group theory is recommended)

Personally I hope they don't find the Higgs particle. If they didn't, all physicists would have *A LOT* to do (that would be fun ). And I don't think they will find anything relating to supersymmetry.