There's not likely to be any further CPUs for AM3+. However, this has not been officially confirmed; it's based on leaked roadmaps that don't have any new AM3+ chips till at least the end of 2014 (IIRC).
FM2+ and AM1 are the current sockets.
However, that doesn't mean that AM3+ is automatically a bad investment. There probably won't be any more chips for LGA2011, either.