ValueRAM. I have it and I overlock fine. I don't want to pay $200 to be able to overclock my RAM, and while I can get slightly less performance for $70. OC'ing RAM helps, but not that much. If you can afford overclocking RAM, then go ahead. It WILL benefit you, very nicely if you can get it really high (250Mhz+). But the performance increase isn't worth $130-something. Like Pzero said, you could buy a MUCH better videocard for that much. And the performance increase from a better videocard is MUCH better than what you would get by getting your RAM to 270MHz or something.
As for the brands. Go Corsair ValueSelect. Its the cheapest (usually) and a very nice brand. Brands don't really matter in ValueRAM, unless they're really crappy no-name companies.