The Winamp equalizers presets are the best equalizer settings I have found. The following guide will get the default WinAmp presets working under Banshee 1.2.

1. Download the equalizer presets
wget http://www.mikesplanet.net/files/equalizers.xml.gz

2. Install equalizer presets in Banshee 1.2 (Please note, this will write over existing presets)
gunzip -c equalizers.xml.gz > ~/.config/banshee-1/equalizers.xml

Yes, this still works in Banshee 1.5

3. Start Banshee, Goto View -> Equalizer and choose what preset you want to use.