This is my first real foray into the world of Quartz Composer, so I'd like to start by sharing these with the community. I created both these gauges using Photoshop and QC, and both work quite well when controlled by audio analyzer bands.
This is a simple indicator with only one needle.
http://www.eximworks.org/storage/quartz_gauge.qtz
More stylish, with three inputs: Centre dial, a blue level and a yellow level that raise and lower.
http://www.eximworks.org/storage/quartz_gauge2.qtz
Lemme know what you think and any improvements I could make!