There's Yongnuo, a Chinese brand out of Hong Kong. Their 568EX is HSS compatible, and will also respond off-camera to a Commander flash in Nikon's CLS system. Yongnuo also sells a range of radio trigger and receivers for off-camera flash as well.
From what I understand from friends who have them, they are confusing to learn, simply because of the really basic Chinese-to-English user guides, but they seem to work, and they cost about half the name brand units. That one is under 200 bucks, for example.
How they compare to Nikon units I couldn't say. Do they produce as much light? I don't know. They have the same features, though, with zooming flash heads, iTTL metering for auto-exposure, tilt and swivel for bounce, along with CLS response and high-speed sync.