The brand new SEIKI brand 4K HDTV has arrived with 3840×2160 resolution for only $1500 on TigerDirect. This is an incredibly low introductory price for 4K HDTV. A big bonus is that it also supports a native 120Hz refresh rate at 1080p!
A user on HardForum has discovered that the SEIKI 4K HDTV can run 1920×1080 successfully at a native 120Hz refresh rate! Confirmed by Refresh Rate Multitool. It also appears to run at higher refresh rates as shown below, though 120 Hz is the maximum supported rate with no frame skipping.