A lot of USB support sites recommend PCI cards with NEC chipsets as opposed to VIA, SIS or ALI, which have, in the past, been known to have issues, that situation may well have changed of course but it's still worth thinking about.
If you have a mobo with a Via chipset, avoid getting a pci usb 2.0 card with a Via chip. This is the combination I have read causes problems. My bad experience was with 2 cheapo Ebuyer cards with Ali chipsets. The replacement Belkin card is fine, and I think is NEC chip based.