YONGNUO Speedlite YN565EX Flash for Nikon i-TTL + Canon too  Tested Exc+. 404  

A whole lotta flash for the money.  I tested this on 3 Nikon DSLRs (D300, D7100, D810) and it handled Nikon TTL perfectly.  Pasted below is some feature information from the web.  This is the EX... there's also an EX II and EX III.  The model for sale here works, at least, with D3100 and earlier, D5100 and earlier, D7100 and earlier, D810 and earlier.  For later Nikon bodies, check online for compatiblity.  This one will likely work on newer Nikons, but may not support the latest flash features. 

A very cool thing noted below is that in _wireless mode_ it can also do Canon TTL.  

Thanks for looking.

(from Photo-Store.net ; Yongnuo Store)

Yongnuo YN565EX is the most popular Yongnuo TTL flash for Nikon users. YN-565EX is a great alternative to much more expensive Nikon SB700 and SB910 speedlites offering the same functions at much lower price. Great flash for professionals and advanced amateurs.