+1 on iZotope RX2.

As an alternative, I have used the built-in one in my version of Adobe Audition 3.0 because sometimes it does a better job. RX2 has a huge amount of control as you of course will know - you can separate out tonal and broadband noise, and lots of other options. Sometimes none of that helps and the simpler Audition one works perfectly. So I tend to go between those two.

Techniques: multipass is a good technique, also inverting so you just hear the output noise, which helps to isolate unwanted birdies in the sound, and finally, reversing the audio before noise-reducing can sometimes give you more to play with while preserving the transients (reverse it back afterwards, of course).

Another thing which can help with interior recordings of musical instruments is to noise-reduce so much that the background completely disappears in quiet passages, then put some reverb back in afterwards - it can fool the ear into thinking you had a really quiet venue.