If photography is your business, buy the 5D Mark II today. Even if the 5D Mark III is announced tomorrow, it won't be available for a while.
Otherwise, if you're happy with your T2i (in my case, I am, even though I'd love full-frame), I'd stick with it for a while, until you feel like you're "outgrowing" it and need something it can't provide.
However, I would not recommend using the 5D Mark III's release as an excuse to just keep waiting. It's a recipe for driving yourself crazy. Think of those people who were and are waiting for the new 500mm and 600mm.
Of course it's your choice at the end of the day. If your fear is the price suddenly dropping, you probably don't need the 5D Mark II right now. And if you have that fear but feel like you need it, buy used and then the price will not drop significantly for a long time and you can resell at almost no loss when the 5D Mark III comes out.