midknight,
If you're looking for a USB stick for your PC, go with the ThinkStick. It's firmware upgradable, high-speed Z-Wave, and only $39.95 MSRP. It's also compatible with Windows XP, 2003, Vista, and 2008 (including 64-bit editions).
If you're looking for a more expensive device for desktop use that you can unplug from your desktop to add/remove devices, and which uses a serial port connection, something like the Z-Troller may be the choice for you.
Please note that we're working on a number of new benefits for ThinkStick--so the value in having one is just going to continue increasing. It really is the premier Z-Wave USB adapter on the market.
Chris