Exchange of products, ideas, and memes is ubiquitous across history and societies. Repeated transactions occasionally leads to "bubbles" where something becomes disproportionately valuable. Remarkably little has been done to explore this highly non-equilibrium aspect of economic activity. We suggest to view "bubble dynamics" in terms of a market of memory and attention. We introduce an agent based model where a positive feedback acting on recent memories is counteracted by a slower negative feedback. We discuss the model in the context of fashion cycles and financial bubbles.