My favorite compressor for bass is Aion's Meridian with bass specs, Guyatone PS-20 clone. It does things other compressors can't do, just check the build docs, you'll find all the details.
Favorite dirt circuit is by far the Bass Amuser, a real tube overdrive designed for bass by the german diy community a few years ago. Surely it's kind of a confidential circuit, far from the industry networks. It sounds much better than every bass dirt circuits i tried so far. Available at musikding and uk-electronic.de
Aion's bass preamp TS-50 is my favorite circuit to shape the sound at the end of the signal chain. Another brilliant design based on a legendary amplifier : Traynor TS-50B bass amp.
GCI N.E.W Bass Overdrive (a boss ODB-3 variant that isn't intended to sound like the ODB-3) has a large range of interesting sounds available thanks to the various controls. Darkglass BK3 (many pcb webshops have their own BK3 clone) is also very popular for good reasons. It sounds great and sharp.
Frantone Cream Puff (PPCB Cream Pie Fuzz), wich is different but somehow close to the Big Muff op-amp, and Moosapotamus 360 Bass Fuzz are my favorite fuzzes on bass. The 360 is also based on a legendary amp's fuzz circuit. Frantone's circuit sounds amazingly good on bass, almost addictive.
About modulation, the first circuit that comes to my mind is Lovetone Meatball (Aion's Spectron). An enveloppe filter. This thing is just incredible.
I tend to use an MXR Stereo Chorus, which is not available in the diy community. My second choice would be Delyk's 2nd Choral, a Boss CE-2 clone with useful mods, able to become a CE-2b (Boss bass version) thanks to a toggleswitch. CE-2 might feel a bit classic and unoriginal, but it sounds always better to my ears than all the many other chorus clones i built during my great chorus quest.
An octaver can be interesting too, i'd suggest Delyk's Up Down Daddy, Pearl OC-7 clone. I think it's more interesting than Boss octaver because it sounds just as good, if not better, and has 2 octaves down and one octave up. It's a tight build, but perfectly doable with patience.
EHX Deluxe Octave Multiplexer is also a great octaver circuit, 3 octaves down and a great fuzz circuit all-in-one, available as Aion's Downtown Fuzz. You can turn off the fuzz if needed, of course. Features also a very effective bass toggle, able to shake the windows .
A tool like Pro-Cessor might quickly get very usefull. Splitter, Mixer, Clean blend, Effect blend, from TH Custom Effects.
I built many bass circuits, but these ones are the best i could find, at least in my humble opinion.