USB Hub External Power
The AC adapter provided is 2A @ 5V - 10W.
What should I use in the car and where's the best/cheapest place to buy?
I'd prefer something inline/hardwired instead of using an accessory socket, but I can chop the adapter if neccessary.
Will any 12V to 5v adapter work, or does it need to be regulated?
I would think any adapter will do, but I'd rather be safe than sorry.
run 5v from the pc psu to it
You can get a 7805 regulator which will output a clean 5v+ from automotive voltages.