The 955 and the 1090T (hexacore) both offer good bang for the buck for Phenom 2 processors. The 1100T hexacore is a good processor for the price as well, but the 1090T has a better price/performance ratio.
And yes, AM3 processors work in AM3+ boards. It's the other way around (AM3 motherboards, AM3+ processors) that don't, besides a select few motherboards. To put it a better way, AM3+ motherboards (Bulldozer mobos) have backwards compatibility with AM3 processors (such as Phenom 2).
That Gigabyte motherboard you linked looks good, and would work very well with anything AM3 or AM3+.