XMS and OCZ are both popular, although if exceeding 230-250 MHz FSB, one can always drop the mem ratio to keep fairly tight timings.
(There are a few PC4200 DDR variants that are supposed to support 275 MHz FSB with decent CAS2.5 timings, but they will cost ya, and most jsut choose to lower the mem ratio to keep the mem freq at 220-230 MHz...)