I'm in the UK. I really like Z-wave, I've now got 4 separate lights, various plug-in appliance controls (valve amp, mood lighting, etc), a smoke alarm (WIP), a PIR motion detector (WIP) and am planning on buying TRV valves and thermostat when I get round to ripping out my poo 70s central heating system (next summer).
I have bought all of my stuff from a chap called Ivor here http://www.uk-automation.co.uk/
he has been extremely helpful to me from the word go. I actually met him a few weeks ago, and he's a very accommodating and approachable guy. He can offer great advice on installation, general operation etc. He can also sometimes get hold of things not on the website if you want something specific.
This is the USB controller that you want http://wiki.linuxmce.org/index.php/Seluxit_viaSENS_Home_Controller
You could go for a cheaper dongle, and it might be alright for a few lights, but if you are planning on making Z-wave your protocol of choice and want to expand in the future, spend the money on the Seluxit.