One other "one stop shop" utility that I recommend for certain smaller builds: SSF's Tool-Box. In 6 hp, you get a halfwave rectifier for waveshaping, an adder, a comparator, a diode OR, an inverter, and a 2-1 electronic switch, all for $149. For those building a specific, targeted synth, it might not be quite the thing, but anyone building a multi-purpose modular can get plenty of mileage out of something like that.