Well ever since I made the move to Corsair I will stick to them with a long time - Keep in mind there are different brands of RAM, but only a few actually make those chips (i.e. Micron/Hynix/Inineon,etc.)
Be careful when buying RAM always check their rating and comapre with your motherboard. By default JEDEC standards, your RAM will run at conservative timings at lower voltage - however if you want to run them at advertized specs your board will need to support the higher voltage. Some boards can only go up to 1.95 while others 2.5V. Some motherboards are also very picky about RAM. I honestly would not use OCZ, I would pick Mushkin or Corsair over OCZ. You will get a lot of different opinions on this.
These are the ones I use
Welcome to Corsair :: XMS2 DHX Product Information
I use the 4 GB 4-4-4-12 kit - They use quality components and so far run great - and they overclock very well.
My previous setup had the XMS2 DDR-2 667 4-4-4-12 which I overclocked and ran 24/7 @ 800 4-4-4-12, and it passed memtest86 burnin, prime95, and everything I threw at it. I'm thinking my new RAM can easily hit 1000 (I'm not condoning or asking people to OC their RAM and only talking about my personal experience!)
Can anybody confirm what does COrsair use in their DHX 4GB 4-4-4-12 kit ? Do those use Mt chipsets ?