Scott,
You want a USB 2.0 PC card that uses the NEC chipset; this is the chipset that is compatible with Apple's built-in software. It is difficult finding out which chipset a card uses; for whatever reason, the manufacturer is disinclined to do so. However, this PC card...
http://www.startech.com/item/CB330USB2-3-Port-Cardbus-USB-20-Card.aspx
...does list the NEC chipset and is only $14.
Will the Mac sleep properly with the card plugged in? It should but I cannot verify so. It will have enough bus power from the card itself to mount/use a thumb drive; having the additional power from another USB port is also nice.
All I can say is buy the card if you want to use USB thumb drives with the higher USB 2.0 speeds. If there are issues, then there are workarounds.