Samsung just announced that the unlocked North American version of the Galaxy S8 and S8 Plus are now available through more retailers, including Amazon and Target, along with some enterprise distributers. The best part, though, is that some retailers are offering steep discounts on the unlocked phone out of the gate.
Best Buy and B&H have the unlocked S8 64GB for $624.99, a phone that is listed for $756 at Verizon. Both stores also offer an unlocked S8 Plus for $724.99, a handset that goes for around $850 at carriers. Amazon hasn't listed the new domestic unlocked models yet, but I would expect it to match those prices. Best Buy's deal should run all week, but I don't know how long B&H will keep the price that low.
The domestic unlocked model has full support for CDMA and GSM-based networks, so it should work well on any major US carrier. International and dual-sim international versions are also available for slightly higher prices. The phones are also be free of the usually app detritus that carriers love to add, and Samsung usually is able to get OS updates to its unlocked models faster than to its carrier versions.