I do not understand why everyone is jumping on the SB bandwagon when it's clear from the OP that a S939-level system is sufficient for the OP's needs. OP isn't complaining about lack of performance - OP is worried about a soon to expire part! Anything from either AMD or Intel is going to be a huge step up from their current system.
OP, if you would rather spend less on your computer than spring for compute power you probably don't even need, I'd simply get a $60 AMD Athlon II X2 250 and a $60ish 880G chipset-based motherboard. If you find yourself needing more power in another year, used quad core AM3 CPUs will be $50. In another two years, used hex core AM3 CPUs will be $50.
It never ceases to amaze me how well-intentioned and otherwise well-informed folks always assume everyone needs the latest and greatest computer components. They're terrible investments.
Sandy Bridge is quite cheap, its also offers substantially more performance. The OP is the one that mentioned looking at a 6 core Phenom II, which is one of the worst values out there right now.
Investments? Ignoring that, for most, a computer is not an investment at all, but if it is, then often extra performance is worthwhile to invest in. Buying likely EOL components (current AM3 boards) are also often terrible investments too.
If he wanted to get away with peanuts, just buy a dirt cheap replacement motherboard for what he's got, no need to even bother talking about upgrading. He however said he wants an upgrade, which makes no sense to recommend something that isn't the best value for his money.
He also specifically mentioned wanting a board to upgrade the CPU. Sandy Bridge is enough that he wouldn't even have to worry about that, but that's also why people said to wait until Bulldozer so he can then find out what performance for what price it offers. Its possible that it will offer similar performance to Sandy Bridge for close to the same price, in which case, buying a current AMD CPU would just be a waste of money.
This. SB (unless you spring big bucks for the 'K' models) is unoverclockable. It's also pricy.
A good, cheap, fast, AMD dual-core or triple-core, with a nice cheap mobo (preferably one that can unlock cores), would be a solid choice. Even better if you win the core lottery and manage to unlock to a quad on the cheap.
There's still a lot of value in AMD rigs at the budget end.
Does the OP have a Microcenter nearby? They have some good deals on AMD CPU+mobo combos, and they are running a special on SB i3-2100 + H61 mobo for $120, while supplies last.
While I would agree, but he's wanting system he'll upgrade, so if he wants to just cheap out now, he might as well just buy a cheap replacement board.
Sandy Bridge is not pricey. Its not dirt cheap, but the only reason AMD is, is because that's where its performance is and its a long in the tooth setup. An i3 is much more efficient and is similar in performance for the price.