If I don't want my bassline to be FM-based, wavetabley or a super Depeche-Modey ARP2600 sound I go for Elektro. TAL knocked it out of the park. The FM knob, roland-type PWM, great assignable LFOs, multiple filter types and filter contour knob with a wide sweep add to the goodness. Think of this as a 2 oscillator SH101/TB303 with the super-fatness of a Moog (courtesy a sub oscillator that is just outstanding) and some extra features. It doesn't simulate any particular synth I can think of, but it is one of the few 80s-inspired bass VSTi plugins that can go toe to toe with good hardware. It might not take on a real moog, but it'll stomp on a lot of 70s and 80s analog synths. It sits in the mix so well. You can do a lot of other stuff with it, and I do, but its a great bass machine for better-than-vintage patches. I use this plugin more and ore for bass sounds that harken back to my childhood but have a little something extra going on.
All that said, I must remind you all what a previous review pointed out: this synth will not replace a more modern synth if you need modern bass on your track. Don't bother unless you intend to Do some multiband or side-chain compression, EQ and maybe add some bass-enhancement. And it wills till be a vintage texture, though a complex one if you are using all the features wisely.
Another freeware VST by TAL, this synth appears to be much more geared toward 80's synthpop sounds, specifically synth bass stuff. I use it to make sub-bass tracks and industrial synth basses, though occasionally I'll use it to make a key or lead tone. It's really good at mimicking some of the tones used by bands like Depeche Mode, especially if you run it through an amp simulator, but it has a hard time keeping up with a lot of modern synth bass textures and tones.