The HTC One M8 is one of the more desirable Android phones available at the moment, and if you're looking to find a good deal on one, "qualitycellz" (may not a be a real name) is happy to oblige on eBay. The seller has at least a few refurbished AT&T-branded One M8 models going for $449.99, a full $220 off of the new retail price at AT&T. You can have any color you want, so long as you want silver.
For a device so new, this is a rare deal - assuming you're OK with the refurbished status of the One M8, you won't find a better price for the off-contract phone anywhere. The seller claims that these phones have been SIM unlocked, which means that the AT&T 3G and LTE bands should work with most international carriers, though getting it to work with T-Mobile's unique LTE bands is probably a no-go. International readers, the seller will ship worldwide... but not to "Africa, Asia, [the] Middle East, Southeast Asia, South America, Mexico, Cyprus, Czech Republic, Greece, [and] Ukraine." So, yeah, looks like western Europe only.
As with most of eBay's featured deals, basic shipping to the US is free, and you can
ignore sales tax carefully add the local sales tax to your state tax return at the end of the year if you live outside California. (Snigger.) The phone has an HTC warranty, which probably means 90 days on the refurb model. Act fast, these kinds of dramatic discounts tend to mean quick sales, and refurbished stock on a phone this new can't be very robust in the first place.