Crazy Ivan's Medieval: Total War section: Offers Croatian and Serbian historical battles, screenshots, scenarios and modifications.
Medieval - Total War: Offers screenshots, downloads, and news.
Total Battles: Offers historical battles (Northallerton 1138, Shrewsbury 1403, Flodden 1513) and maps (Alrowan castles) for MTW and La Haye Sainte farm for Napoleonic Mod.
Wikipedia: Open content encyclopedia article covering gameplay, factions, buildings and units.