Well many good complex VCOs have already been mentioned, for example the DPO of Make Noise, it's high on my wish list too.
ACL's Variable Sync VCO or Multi-Function discrete VCO are options to keep in mind. Now don't laugh but the Doepfer - A-111-2 High End VCO might be a good option too, this isn't a simple VCO and offers a lot for the money. I have this module and I am really happy with it.
If it is your cup of tea, you might want to consider the Intellijel's Rubicon2. I got it, but I am actually not sure if this one is worth the money, it can do fantastic things and you really get a complex VCO, but is it worth it for what you are paying here? I am not too sure...
Not extremely complex but a lot of fun, at least for me, is the E330 - Multimode VCO from Synthesis Technology, I like that one.
Already mentioned the Endorphin.es - Furthrrrr Generator, I had it tested two times at my local dealer. The first time I just didn't manage to get any sound out of it at all, no idea if it was broke or I just didn't know how to use it. The second time it kind of blow my head clean off, this is a nice generator, bloody expensive but from all that expensive stuff out there this one might be worth it I think, it's high on my wish list too.
That having all said...
I wonder if I am the only one here but is it worth it to pay say 600 or 800 bucks for a "complex oscillator"? For many of those complex oscillators their prices are in the region of some serious good and complex sequencers! Those expensive sequencers are already far too expensive, if you would ask me. So I am not 100% convinced yet about some of those serious expensive complex oscillators.
The DPO (haven't tested it yet though) and the Furthrrrrr Generator might be the exceptions but the rest, is it really worth that kind of fortune? I am not sure.
Give it a very good thought before you buy such an expensive "complex" (or should it be called "expensive") oscillator! Better have it tested at your local dealer first!
Take care, have a good weekend and kind regards, Garfield.