Paul,
You must have read my mind. I hesitated about mentioning it for one main reason - I use the freeware 3.0 version (I'm a cheapskate!) and the frequencies displayed are not totally 100% accurate.
I agree, it's a great tool though.

It's a bloody disaster for new-comers, that the FS Navigator Site has finally closed down...

...!
I've been using it, (the payware/registered version), for every version of Flight Sim since FS '98, and without it I wouldn't have progressed up to FS 2004....
...trust me...

...!
I would have concentrated more on Hoovering, dusting the furniture, and mowing the grass, etc, etc...

...!
Its fun to see other Flyers, on-line, using it...

...!
Its the main reason why I fly with FS 2004 and FS Navigator every day...

...
...So much joy should be made a Criminal Offence*....

...!
Paul...G-BPLF... 8-)...!
* ....perhaps?...

...!