The other 5 playable teams will be Barcelona, Arsenal, Marseille, Dortmund and AC Milan. It is unclear whether the teams will be fully updated, and I suppose that will partly depend on whether a deal taking Samir Nasri from Arsenal to Manchester City is ever finalised.
Manchester City were the 8th most played team in head to head online games in Fifa 11, and it will be interesting to see if that rises any higher up the table in the next 12 months as the recent multi-million pound deal with EA (amongst other notable deals) and Champion's League football will undoubtedly raise the profile of the club considerably during the 2011-12 season.
The full game will be out on September 30th. I know which team I'll be using.