L1 cache

but as to what i think you're actually asking about
pc1066 rambus has 4.2 GB/s bandwidth
dual channel ddr 266 has 4.2 GB/s bandwidth
ddr 200 is 1.6 GB/s
ddr 266 is 2.1 GB/s
ddr 333 is 2.7 GB/s
ddr 400 is 3.2 GB/s
as far as which chipsets support which:
granite bay(P4) and nforce2(axp) support dual channel ddr, but athlon systems don't gain much from the added bandwidth as it exceeds the fsb bandwidth(unless integrated graphics are being used)
kt333 and kt400 support ddr333 and ddr 400 respectively for athlon, nforce 2 can also run single channel (not sure about granite bay...but if your running p4 single channel just get an 845 chipset as the board will be cheaper)
intels 845 chipset supports ddr 333
i'm not really up on rambus chipsets beyond the 850
as far as ram brands go i like corsair and crucial, and reccomend staying far away from OCZ