Hi Mark.
Some of the most common ones:
Brightness - how "sharp" something sounds. i.e. if there is too much treble (cymbals/tambourines are so sharp they hurt the ears) then it might be "bright", whilst not enough is "dull"
Soundstage - imagine you are at a Beatles gig, with the Ringo in front of you, John on the right, and Paul/George on the left. If you close your eyes, you would still be able to tell where they were, right? The same applies in HiFi. A good soundstage will let you pinpoint where each performer is performing from. Obviously, this also depends on the recording.
I'm sure there are some more, and that someone else will chip in with them...