I do a lot of songwriting, and for a record I'm working on I'm putting together a bunch of demos to look over and eventually pick which ones I want to flesh out and produce. 

Some of the music I do is electronic in nature, a little bit of disco and new wave, and I've been looking for a VST guitar plugin that sounds pretty believable. I haven't yet found one that I'm completely happy with, but does anyone know of one? 

I know it's probably easier to just have someone play guitar on the demo, but where I am and with the limited gear I have that's not a feasible option just yet. 
MarkLykkos I really don't think you are going to get a convincing sound programming guitar or playing it on a keyboard. There are so many little variables in guitar playing that you cannot really have MIDI perform (picking delay, fret noise, plucking differences, etc). Further, the guitar voicing has a lot to do with the instrument's natural inversion requirements, keys does not require such inversions.

I would suggest to find a synth voicing that will fill the role you need, or just have someone track real guitar for you. You could probably get someone on Fiver to help you out.
Lepou plugins are free, and sound good. If you have the budget, Line 6 Helix native is coming out soon and will be the Helix in plugin form. 

Scratch that, you want an vst instrument, and yeah that will never sound convincing