A couple things to get the ball rolling:
The magic DUSG, IMO one of the main centrepieces of the Serge system and philosophy. It can be a filter, vca, oscillator, lfo, trigger generator, delay, slew, function/envelope, and more.
http://carbon111.com/alphabet1.html – more details on some patch ideas fort he DUSG.
It’s really at the heart of Serge’s “patch programming” notion - being able to patch a module or set of modules for specific functions at different times.
When I’m done building my system I’ll have 4 DUSGs in it, and I’m not sure it’ll be enough 
There’s a euro-serge version from Random*Source, and there are lots of modules inspired by it (i.e. Swoop, Maths/Function).