Specific to Amstrad XTs

• Cliff Lawson's Amstrad site: XT section
• Cliff Lawson's Amstrad site: XT system discs
• Information and pictures for the PC2086
• A site dedicated to the PC1512
• Paradise VGA drivers. Use PVGA16-1.ZIP and PVGA16-2.ZIP for the PC2086/3086 Paradise chipset.
• The PPC640 service manual (8Mb download) at 1000bit.net.
• Aporia (download aporia14.zip from the linked page) makes Windows 2.x almost usable. If you're still using the copy of Windows that came with the PC2086, I recommend installing this utility.
• Notes and drawings for building a PPC expansion box.

Links covering other XTs as well

• Multi Emulator Super System emulates various XTs, including IBM's own, the PC1512 and the PC200.
• So does PCEM, though since it's Windows-only I haven't tested it.
• Games for DOS.