MXR built a whole line of rackmount stuff, with the Pitch Shifter and the Flanger being great examples.
Ibanez built some killer gear: their UE400s combined 4 stompboxes in two rackspaces with a proprietary footpedal. They also had the AD202 delay which is studio worthy. They segued into partial digital/analog programmable rack stuff and then dropped it.
DOD built both a flexible reverb and a cool rackmounted delay in single rackspace enclosures (got both for sale, actually).
ADA built a bunch of rack stuff, partly analog and partly digital-single rackspaces, complex routing, wonky switches-hilarious!
Eventide started with the 910? Combined digital pitch shifting and ?analog delay.
Yamaha has the "table top" two rackspace E1005 and 1010 delays-arguably the best analog delays ever made.
Peavey built the Valveverb (reverb and tremelo, killer) and the Spectrum digitally controlled analog filter and envelop generator. Both long out of production and getting hard to find.
I've got a Maxon UE401 I scored on fleabay for a couple bills, it's rackmount with a killer OD, chorus/flanger (switchable) compressor, and phaser all for $200. Circuit-wise they are almost all identical to the x0x-series counterparts except with more complex switching, and different (better) buffered in/outs.