I've comes across quite a few references to aspects of Roman culture which are identifiable as being 'pop culture', even if not in a directly modern sense, but I don't know that I've ever seen mention of anything vaguely recognisable as such in the post-Roman period (in the West, at least) until comparatively recent history. I generally don't subscribe to the 'dark ages' concept, so I'm curious... Did pop culture cease following the Roman period? If so, when is the next time we see something identifiable as such occur in the West?
When you write "post-Roman," do you mean the early middle ages? A lot of the art and culture that has been preserved from that period is sacred, partly because the institutions recording everything were affiliated with the church. You can't really separate religious life from everyday life in this time period (or magical and "real," for that matter), so your question about "pop culture" makes some assumptions that won't necessarily apply to this era. That said, there are a lot of examples of what might be called "pop" culture -- preserved in songs, song texts, folk tales, and visual art. You might be interested in the Carmina Burana (not the Carl Orff music, though), Roman de Fauvel, Perceval, works by Christine de Pizan, the Jeu de Robin et Marion, Beowulf, the poetry and songs of Guillaume de Machaut, and the Roman de la Rose. The Carmina Burana are collected songs of wandering scholars, often dealing with themes of games, drinking, sex, and social criticism. The Roman de Fauvel is a satire making fun of the corruption of those in power, and it was wildly popular.
You may also be interested in popular religion and piety—the cults of the saints, pilgrimages, the Peace of God, etc.