Here's another (mostly) single-manufacturer example of a monosynth-type rack. Explanations below.
Overall, the goal was to recreate something similar to a Dotcom starter rack, but in Euro. I went with Intellijel's 6HP modules because of their balance between size and user-friendliness, and for a uniform aesthetic. The Mutable modules were added mostly because they provide a huge variety of very space-efficient utility functions, without looking too out-of-place.
From left to right:
(4HP) - Basic power interface module for cases that don't have power connections on the back or side. If you've got a case with built-in power, then I'd probably drop this and replace the µVCF (6HP) with a Polaris (10HP), for additional filtering possibilities.
(6HP) - A fully-featured monophonic MIDI-CV converter module that takes up a minimum of space. The 16th-note clock divider output is useful for triggering the Quadra, and the 4 CC channels (bender, mod, velocity, and user-assignable) give you a huge range of expressive control from an external keyboard. If you're not a keyboard player, or if you're using a controller that already has CV outs, then you could replace this.
Mutable Instruments Links
(4HP) - You get a buffered multiple (perfect for precision routing of pitch CV to the 3 oscillators), plus a pair of mixers: a 2-in/2-out unity summer (which could also work as a second multiple for signal routing), and a 3-in/1-out averager that reduces the likelihood of clipping with hot signals. This is a great space-efficient utility module, and it ensures that you'll still have mixing functionality available even if you're using all three Triatt channels as individual attenuators or inverters.
Mutable Instruments Kinks
(4HP) - This gives you some signal- and clock-warping options, plus an always-useful source of randomness. The top section (Sign) gives you some versatile waveshaping options: inversion (useful for CV, particularly Quadra envelopes), half-wave rectification, and full-wave rectification (the latter two being particularly well-suited to modifying waves from the Dixies). The middle section (Logic) provides basic OR (max) and AND (min) functions, with the benefit that they can also operate on continuously-varying analog signals, not just on gates or triggers. While the µMod makes this section somewhat redundant, it's still useful to have in case you want to dedicate the µMod to good old-fashioned audio-rate ring modulation. Lastly, the sample-and-hold (S&H) section gives you the quintessential random source, complete with a built-in white-noise generator. Use it to add a noise element to drum or woodwind patches, use it as an analog bit-reducer, or use it for traditional stepped-random modulation.
Intellijel Dixie II
(6HP x3) - A basic analog oscillator with six wave outs. There's no pulse-width control onboard, but you can use a Triatt channel into the PWM input to effectively give you a pulse-width knob. (Mult it to all three Dixies if you want to keep things synchronized.) Three oscillators is a great number for a beginner's system, as it lets you use one as an LFO or audio-rate FM source while still allowing for traditional 2-oscillator patches.
Intellijel µFold II
(6HP) - Probably the one module I'm least sure about in this rack, because it does pretty much one thing (wavefolding), and one thing only. But that one thing isn't found on very many monosynths, so it's a cool introduction to the sorts of sonic effects that you can get from the modular world. But if you think there's enough signal-mangling in this build already, you wouldn't go wrong swapping it for another VCA module.
Intellijel µMod II
(6HP) - The ring modulator is a classic synth circuit, and for good reason. This one adds continuously-variable analog logic outputs for additional signal-mangling fun, and works on both audio and CV signals. You can also use it as a straight-up VCA, if both your µVCA channels are already occupied.
(6HP) - You get a three-channel inverting mixer which allows for each of the three channels to be decoupled from the mix and used individually, if you just need extra attenuators. The input of each channel is normalled to a voltage source, so if you don't plug anything in to a channel, you can use it as a knob to control a function on some other module (like pulse width on the Dixies). A classic problem-solving module.
(6HP) - Maybe not the most characterful filter around, but it's both compact and versatile. Unlike a lot of other filters using the state-variable topology, the µVCF can also serve as a sine-wave oscillator, if need be.
(12HP) - Four channels of envelopes or (unipolar) LFOs, at effectively 3HP each. Perfect for all your modulation needs. Note that, if you want an envelope to be affected by velocity like on a standard keyboard synth, you'll need to run it through a VCA channel, and use the velocity CV to control the VCA's level. Intellijel's Dual ADSR has these VCA channels built-in, but takes up an extra 2HP and only offers two envelopes to the Quadra's four. On the whole, I'd say the Quadra is useful in a wider variety of patching approaches.
Intellijel µVCA II
(6HP) - Two channels of voltage-controlled attenuation that (in the more recent revisions) are normalled together, allowing you to use this as a two-channel voltage-controlled mixer. It really is true:
(6HP) - Another module that I'm on the fence about. Having a built-in headphone jack can be really nice, but output modules aren't strictly necessary. If you're planning to run your modular straight into a mixing desk, you could easily dump this for another VCA.