Looks like Sona and Mordekaiser top the votes as most overpowered in the informed opinions of the LoL community.
http://www.leagueoflegends.com/board...d.php?t=332106
EDIT: Search youtube for WCG2010 League of Legends matches. The ones involving US and now world champions, CLG(US) vs SK(Germany/Europe) in the grand finals are really interesting.