Some more reputable (and easier to deal with retailers) in the USA:
- Best Buy (in store and next day pick-up online order) 30-day no hassle no restocking fee return policy (45 day if you are a premium rewards member)
- Amazon.com
- Tiger Direct
among some other online custom makers like ExcaliberPC and XoticPC. I'll post a link to the product page with the list of retailers if I can find it again.
Edit: Here's the link I was referring to:
http://promos.asus.com/US/2012GSeries/