I beat the Elite Four earlier today.
The Elite Four themselves weren't too hard since I had type advantages. The champion was tricky since she had at least 3 dragon-types. (Not to mention my Gigalith's Stone Edge failed 3 times in a row...)
At any cost, beat her Haxorus as quickly as possible. It will keep using Dragon Dance to raise its speed and attack to instant kill you without you being able to attack.
Anyway, here's my team that beat them: Serperior, Zoroark, Genesect, Reuniclus, Mienshao, and Gigalith
If you want, I can tell you who the champion is and what Pokemon she has.