I just recently learned about the Electro Harmonix Knockout EQ for guitar and bass. The first video on this demo page shows how this effect can make a Les Paul sound more like a Strat or make a Strat sound more like a Tele.
http://www.ehx.com/products/knockout
definitely looks like a useful effect.
the description says it is a 7 pole filter for the low mids and a 6 pole filter for the high mids, and then a blend control for the wet/dry. Has anyone ever tried making a JS version? Would be a great js effect to have access to.