Interesting that, always wanted to have a go at Civitas Dei especially since he (and Boethius) were like an intellectual farewell to the ancient world aside from important guys and philosophical underpinnings in the medieval one. There are a bunch far more minor figures, though worth a quick look, writing a little later. Hydatius wrote a chronicle about 20 years after Augustine died (might be downloadable in English) from his backwater in Gallaecia, Hispania, which was under the Sueves. He kinda thought the whole of society was falling apart, pretty dark volume. Victor of Vita (History of the Persecution) wrote in Carthage about Vandal cruelties (somewhat a clerical bias thing since the average Joe was likely no better or no worse under the Vandal kings) and Gildas wrote On The Conquest and Ruin of Britain, which, aside from a lot of pastoral stuff in full of over the top, sometimes funny, invective. On local king is described as the "Vulgar whelp of a [Cornish] lioness" and I think there was a line "Kings Britain has but they are tyrants, priests Britain has but they are fools, leaders Britain has but they are thieves." This was the only record written by a Briton for 200 years or so. Common theme seemed to be that sins had brought about the turn of events and let the barbarians take hold, though this reflects elite anger rather than massive population displacement. Still, 100 years later when some level of accommodation or assimilation had happened in many places like Spain and Gaul (except Italy) the writers tended to sing praises of their new bosses and how they "walked with God"). Very interesting period for me and I try to check anything that looks good.
Below is a good book, mostly complete and free, on Google books called Late Roman Warlordshttp://books.google.com/books?id=7iNqpYo9Qd0C&dq=late+roman+warlords&source=bl&ots=m6NtkE5DwX&sig=pc9Zfflj7FcxKS916K_EDLW_kvs&hl=en&ei=V9TCTL6YOoq8cPKW1cwN&sa=X&oi=book_result&ct=result&resnum=3&sqi=2&ved=0CB0Q6AEwAg