Hey Jayson,
First, I would like to note that the best graphics card for the money article that Jack posted was written in early December when there was a shortage of 4850s. If you read it you will see they have note about the 4850 at the $100 range. Prior to that time the 4850 was the clearly the obvious choice at a hundred dollars--because it is as powerful as a GTS 250 but costs less.
Also, Gddr3 memory is faster than Gddr2. The type on the card will not matter for your compatibility. All that matters is that the card has a PCIe x 16 interface, and that it does not use more power than your system has available. Even though its not a great PSU, your power supply looks ok for the cards we are discussing here.
The 4770 is at low inventory right now--so prices have risen. Its really only worth $99--but is selling at $115. Its overall performance is a little below a 4850. It has a slower graphics processor, but uses super fast ddr5 ram to try to compensate. This card is the most power efficient of your choices, but not the best value for the money.
The GTS 250 isnt quite price competitive with the 4850, but is another Nvidia card with physx if that is something important to you.