Across the Top End (Kimberly, Kakadu, Arnhemland, Cape York and even in the Centre), there are some great "tours". Unfortunately you generally need to pay, unless you know someone, but it is money will spent.
Its also worth keeping an eye out for community Open Days, or public cultural events which run occasionally. I'm not sure if or how they are advertised, but we've been lucky to stumble on one.
We've done the croc boat too, I guess I'd call it a once in a lifetime experiance - I've done it once and it was good, but I don't need to do it again.