According to the ArenaNet-authored pre-purchase retailers list on the Guild Wars 2 wiki, Best Buy has joined Gamestop, which makes them the only two brick-and-mortar outlets in the US that are selling physical copies of the standard edition and Collector's Edition. US players also have the option of pre-purchasing a boxed standard edition through Amazon.
ArenaNet will open the doors for Guild Wars 2's pre-purchases and pre-orders tomorrow, April 10th, and will post the pre-purchase list on the official website at that time. President Mike O'Brien recently clarified some of the finer points regarding the pre-purchase program.
[Thanks to Ravious for the tip!]
[Updated: ArenaNet has also released a Collector's Edition video to celebrate the impending pre-purchase date! We've embedded it after the cut.]
[Updated on April 10th: Tipster Mcguffn has pointed us to a thread in which Best Buy representatives posted that the retailer will not be participating in the promotion, but ArenaNet has since Tweeted that "Best Buy is participating in the pre-purchase program, and will have copies soon. Forum poster was misinformed." We'll update this post if we learn more.]