A filter bank is always nice. The Serge ResEQ is popular and has a lot of character and charm.
That ResEQ is gorgeous and it now feels inevitable that I'll have to find room for one at some point
As for filters, definitely get one with enough room to have fun - this is one of those things you'll always fiddle with and it needs to be accessible. Personally, I'd look at a dual/stereo one or even one with more resonant peaks (like the QPAS or the Vostok Atlas)
Loving the Atlas. Looks like you could get very creative with it. Another great recommendation
One thing I like to use a lot for effects is a Moog Mavis synthesizer, which can be taken out of its enclosure and mounted in a Eurorack case.
-- Zacksname
This is kinda leftfield, and something I really hasn't considered but I like the idea.
Thanks for all your suggestions.