So is there a collective agreement on who really is a great ninjitsu instructor?
I could also give a lengthy post.... so instead, I'll simply link to a few prepared earlier!
http://martialtalk.com/forum/showthread.php?t=86804
Read through that, it deals with what Ninjutsu really is to a small degree, including who to look to (organisationally) if you want to learn this art. The big thing, though, is that the instructor makes a huge difference, most of all in an organisation such as the Bujinkan. And if we were to simply list a collection of names, how would that help you? If I tell you about Tim Bathurst, Nagato Toshiro (both Bujinkan), Troy Wideman, George Kohler (Genbukan), Adam Mitchell, or Manaka Unsui (Jinenkan), or even some of the better split-off instructors that I know of, as well as the various Toshindo instructors, does that help you? Nagato is in Japan, Tim is in Australia, others are dotted around the world.... are you willing to move to where a recommended instructor is, with no guarantee that they will take you as a student? Really, if you are after Ninjutsu, check who is in your area (from one of the legit organisations), and then check out the classes.
But I will say one more thing. The correct spelling is N I N J
U T S U, not N I N J
I T S U. Simply put, "jitsu" is a completely different word to "jutsu" in Japanese, and is not the correct one. The variant "ninjitsu" is used pretty much exclusively by those with no real understanding or knowledge in these arts, so if a school you visit uses that spelling, steer clear of them.