A library for accessing Amazon S3 from Go.
Yes, this is a solved problem. In fact, I solved it many years ago for Java (then Amazon came out with their own API). But it makes for an interesting, small-scale project to (1) see how well an object-oriented design translates to Go, and (2) play with some of Go's features.
Plus, I agreed to do a talk at the Philly GoLang meetup, and needed to come up with something.