Alesis Wedge (2)
These processors didn't last very long on the market, so you can find them very cheap. The reason they failed was not because of their sound, but because they have a very strange table-top form factor. The reverb is second-to-none if you happen to find one. I use them often.

Alesis QuadraVerb GT

I don't use this processor much anymore, but it provides all the usual effects (reverb, delay, chorus, flange, and so on) along with some very interesting preprocessor effects, such as distortion, cabinet modelling, etc. I find a use for it from time to time which makes it worth holding onto.

Alesis MidiVerb 4

I started with the wedges, but wanted a rack version. The MidiVerb 4 fits the bill as a more "modern" version of what I used for years in the Wedges, but in a rack form factor. Thanks, Alesis. I love the sound of Alesis reverbs... It sounds so natural and smooth.

Behringer Virtualizer Pro (2)

This is a very low cost multipurpose processor. I use it for, you guessed it, the traditional effects you find in all processors, except that I don't have to take out a second mortgage to finance it.

Electrix Filter Queen (2)

If you can find one of this beauties, buy it immediately. This company folded from what I think was just bad marketing, but the processors are amazing. It's an entirely "true analog" signal path and provides many different filter types. The only problem with this processor is that it has no way to control the cutoff or resonance via midi. There is a "foot pedal" plug, but a controller was never released. Someday I might mess around with it and figure out how to make a controller for it.