Plucksynth is a fairly advanced physical modeling guitar simulation which was made in 2008 as part of my Msc. thesis. It haven't received much attention in the plugin community, but it is well worth trying it out so I mention it here. A copy is available here. Please notice that this plugin is not intended as a professional final product (It may crash and it will hog your CPU!). Rather it is a research project concerned with sound quality and modeling methodology.