if your looking for a budget build the fx series has great performance for the dollar. sandy bridge is a great consideration as well. more details would help budget/use of the computer ect. i built a 2600k gtx 570 8gb corsair ram vertex2 ssd for under 1300 as a gaming rig works great just look for the deals. if you have already bought the board you would have limited yourself patience is a great virtue with building pcs especially when there are so many performance cpus, gpus, and ram that are so cheap and reap such awesome performance.
AM2+ processors...yes there are a couple. The fist Phenom II's, the 920 and 940. These are not AM2 processors, they are based on the newer Phenom II core, but only support DDR2 memory....they don't have a DDR3 memory controller. And as stated already I think, AM2+ processors WILL NOT work on an AM3, or AM3+ socket, the pin out is different(although AM3 processors will work on an AM2+ motherboard if the BIOS supports it). I just happen to have a PII 920 around here somewhere, was my first PII processor.
All CPUs based on K10 before AM3 was released were socket AM2+, most of these were labeled as Phenom I processors, a couple Phenom II models, and a few Athlon models that were die harvested from Phenom I. AM2+ had a faster hypertransport and support for higher memory speeds than AM2, it was a tweaked AM2 socket designed for Phenom I. Most AM2+ motherboards have BIOS support for AM2/AM2+/AM3 processors. The pin layout between AM2/AM2+ was identical too.
AM3 changed the pin layout so that AM2/AM2+ processors couldn't physically fit, and that is because AM3 added support for DDR3 memory. AM3 processors had a DDR2 and DDR3 memory controller so they could work in a new AM3 board or be used as an upgrade for AM2+.
Than AM3+ changed the pin layout again because FX isn't backwards compatible with AM3.
AM2 supports AM2/AM2+(with BIOS updates)/AM3(with BIOS updates but few boards have them)
AM2+ supports AM2/AM2+/AM3(with BIOS updates)
AM3 supports AM3(a few AM3 boards used the AM3+ socket before AM3+ was officially released so they do support AM3+ processors)
AM3+ supports AM3/AM3+
"Socket AM3 processors are able to run on Socket AM2 and AM2+ motherboards with appropriate bios updates, but not vice-versa. AM3 processors have a new memory controller supporting both DDR2 and DDR3 SDRAM, allowing backwards compatibility with AM2 and AM2+ motherboards. Since AM2 and AM2+ processors lack the new memory controller, they will not work on AM3 motherboards."
Also this AM2+ motherboard that has slots for DDR2 & DDR3 RAM states only AM3 chips work with DDR3 http://www.asrock.com/mb/NVIDIA/N68C-S%20UCC/?cat=Speci...