Aonomus over at Procrastinatus has a LM3915 Based Spectrum Analyzer project in development that has been described step by step. The schematic is almost done and will be released soon.
"I have schematics mostly drawn up for a LM3915 based spectrum analyzer using Fliege bandpass filters to give me bands at 60Hz, 150Hz, 400Hz, 1kHz, 2.5kHz, 6kHz, and 15kHz."
http://hackedgadgets.com/2008/07/30/lm3915-based-spectrum-analyzer/