This is my current monophonic synthesizer system: two Korg ARP Odyssey Modules - one master and one slave using the Trig, Gate, and CV jacks - with both units running through a Zoom MS-70CDR effects pedal and controlled by a Nectar Impact GXP49 Keyboard. It's a tidy little system and is easy to program, especially with the modules now resting on a long music stand and tilted to a convenient angle.
I just bought the keyboard controller last week ($190 at Sweetwater). It has a moderately cheap feel, but it's really not too bad. I decided to buy it because the keyboard I actually wanted - the second version of the EXTRA DELUXE Sixty-One 61Key Midi Controller (see page 15 of this thread) - is still nowhere to be seen, and the company has not responded to my several emails. So, I went ahead and bought a probably temporary keyboard that wouldn't cause me too much financial grief.
I bought the Zoom effects pedal several months ago. It's pleasantly surprised me with its quality, and I would consider buying a second one for my Prophet '08. I'm using it primarily for delay and chose it because it's very reasonably priced ($150 at Sweetwater) and has an excellent vibrato effect that can allow the Odysseys' single LFO to be used for pulse width modulation. In other words, it can be used as a second LFO. Plus, it has stereo inputs and outputs, which allow the two Odysseys to run through the same device and have synchronized modulation/effects.
With minimal resources for this system, I had to thoroughly study the instruments available to me for a full year and make my decisions carefully. The end result is definitely worth it. This is a fine little mono synth system, and I have no regrets about each component in it.
Is this system permanent - relatively speaking? Who knows? It would be a cinch to replace any of its components. I could eventually upgrade to a better five-octave keyboard or insert a better effects unit. But most interesting will be the appearance of the Korg ARP 2600M. If that instrument is around for several years, I could imagine one (or two!) becoming a part of this system. And that's the beauty of it - the flexibility. For now, though, I'm very happy with my Odyssey system, and the only necessity that remains is using it to make beautiful music.