Yes the 2x 512 setup is a lot better.
Here is my suggestion:
http://www.newegg.com/Product/Produc...82E16820145450
Defenitely in your price range and its CL2 RAM so nice and fast, lifetime warranty too. If you are not into overclocking then you dont need anything faster than DDR400. You can use faster RAM cause it runs at slower speeds but why if you dont need to.