Repertorium Geschichtsquellen links any online resources that might exist (edition, translation, scholarship) for medieval texts. Obvious German preference.

If England suits your fancy, the Medieval English Genealogy site catalogues online editions and translations of English records and rolls.

For chronicles especially, a lot of the availability will be 19th century editions/translations on archive.org, so it's often worth checking through Google if you come across a particular name that sounds like an interesting read.

Those are modern publications/editions. If you're interested in digitized manuscripts and incunabula (printed books before 1500), there is another whole world of resources to explore.

If military history is your bag, DeReMilitari.org has a primary source section. It's mostly excerpts from chronicles (in English translation) describing famous battles and sieges.