#1
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. 
#2
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.
#4
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