Get the 630. When the 620 first came out, there were a lot of threads asking "620 or 550 BE?" It usually ended up being the 620. Today, the majority of new games would make better use of at least one extra core than they would from the extra cache.
On the other hand, if you enjoy overclocking and risks, the Phenom IIx2 has an unlocked multiplier and you might be able to unlock one or two cores, stable if you are lucky.
Another option is the Athlon IIx3 440. 3GHz, 3 cores. Currently the best gaming CPU for your money. The majority of games don't use more than 3 cores (I know MW2 uses up to 3) and this CPU is less expensive. Usually around 70-80 USD.
I recently had the same choice and went for the 550BE and got lucky unlocking all 4 cores and over clocking to 3.55GHz. If you want to take the chance and are planning to get a board that supports it go for it otherwise go for the Athlon x3 440 the extra 200MHz will be better than a 4th core in most games.