The Galaxy S5 has been out for a few months at this point, but while everyone is fawning over the Note 4, you can snag a good deal on the GS5. An unlocked AT&T-branded Galaxy S5 is for sale on eBay Daily Deals right now for $419.99. It's an open box, but that's still a killer value.
An open box device is simply one that was purchased and returned to a retailer or carrier. It contains all the original accessories and the device has been inspected for damage. It's not quite new, but pretty close. The device from this listing is the AT&T variant (SM-G900A), but is unlocked to work on any compatible GSM network. The LTE bands for this model appear to include 850 / 1700 / 1800 / 1900 / 2100 / 2600. So it should pick up LTE on T-Mobile, but HSPA+ only in re-farmed markets.
The price includes standard shipping, and there's no tax unless you're in New York. The seller will ship internationally, but you'll be missing some cellular bands.