PCj’s Machines – great for image files of old OS’s and software, with built in emulator on the website – especially great for period correct Compaq Dos and Compaq Configuration Utility image files.
VOGONS – Very Old Games On New Systems – as well as info and advice on vintage hardware and software. Highly recommended.
VCFED – Vintage Computer Federation – another amazing resource for vintage computing, however you typically get a quicker reply at VOGONS.
Phil’s Computer Lab – Amazing site for tutorials, Cyrix driver files, bundled essential software and more.