DDR? DDR2? What speed? What latency-rating? Branded or unbranded? ECC or non-ECC?

So far, I've used non-branded non-ECC DDR with an unspecified latency rating, bought from Scan Computers, since it's just up the road from me (£53 for a single 1GB PC2700 chip), but with my new computer, I'll be getting 2 * 1GB PC3200 cas-2-3-2-5 OCZ Platinum paired chips, £233 for the pair, from OverClock...