The Mutator is great, but expensive. It is also just a 24 db transistor ladder lowpass. I think the Oalkley might beat it in a side by side test, but thats jsut because the Oakley has the Q compensation. Although some of you out there might like the sound of your VCF getting quieter and quieter and you increase the resonance, then you should go with the Mutator. The only Filter Bank that ever seemed worth the money to me is the Sherman, but thats just because it had Midi, and that was when I cared about midi. A filter bank is a very simple thing to make, especily if you build it modular. And now for the Links that I forgot in the last post, just a few off the top of my head for now.
EDP Wasp Filter Clone with Envlope and LFO, A simple little VCF with HP, LP, BP, Notch and a distortion thrown in for an extra $0.50
http://www.oldcrows.net/~jhaible/tonline_stuff/hj_wasp.html
MS20 VCF and other along with a bunch of other fun stuff. The MS20 VCF can be made HP quite simply or even switchable between HP and LP, so a pair of these in a box can give you a wide range of filter responses
http://www.uni-bonn.de/~uzs159/
Then there are also all the Kit options if you prefer.
Oakley http://www.oakleysound.co.uk/
paia http://www.paia.com/
Blacet http://www.blacet.com/
MOTM http://www.synthtech.com/
and there are many others. searching about for synth diy site will give you many more filter choices. Or you can try the Synth-DIY mailing list, you should get a whole lot of responses over there. They really like to talk about VCFs.
adam