Beefy VCOs with a twist, hm? OK...try some of these on for size in your build:
Instruo Cs-L, tona, troika
Dove WTF Oscillator
Make Noise STO (yep! good choice), DPO
Pharmasonic Digisound VCDO (I have the original...quite neat...you can step thru the fixed wavetables)
Pittsburgh Lifeforms Primary VCO, Lifeforms Double Helix Oscillator
Erica Black Wavetable VCO
Studio Electronics QUADNIC, GRAINY CLAMPIT
VOID Gravitational Waves (probably the cheapest complex VCO)
Mannequins MANGROVE
Synthesis Technologies E340 Cloud Generator, E350 Morphing Terrarium, E352 Cloud Terrarium
Moseley Cosmopolitan
Intellijel Rubicon II, Shapeshifter
WMD Phase Displacement Oscillator mkII
Harvestman Hertz Donut mkIII, Piston Honda mkIII
Sputnik Dual Oscillator
4ms Spherical Wavetable Navigator
Rossum Trident
Hexinverter Mindphaser
1010 Music Waverazor
Trying to stay under $600 here. But this is a good cross-section of some of the more capable and interesting VCOs out there. You'll notice that some of these are actually not single VCOs, also...there are several dual oscillators (some in Buchla-like "complex" arrangements), a couple of triples, and the six oscillator 4ms module. Another not expensive thing you might add alongside one of these and your existing VCOs would be a Doepfer A-196 PLL module, which is a strange little thing (VCO, filter, phase-lock loop) that can do glitchy, sync-like behavior while tracking the audio of another VCO. See what works!