It appears that none of us suggested exactly this in response to Timothy's call, but a group of authors from Germany, Denmark, and Australia have committed to make it happen: "The Open Graph Archive: A Community-Driven Effort."

From their conclusion:

We advocated the need for an open, worldwide graphbase to collect and distribute graphs and programs for their generation, analysis, manipulation, and drawing.

And here is their Abstract:

In order to evaluate, compare, and tune graph algorithms, experiments on well designed benchmark sets have to be performed. Together with the goal of reproducibility of experimental results, this creates a demand for a public archive to gather and store graph instances. Such an archive would ideally allow annotation of instances or sets of graphs with additional information like graph properties and references to the respective experiments and results. Here we examine the requirements, and introduce a new community project with the aim of producing an easily accessible library of graphs. Through successful community involvement, it is expected that the archive will contain a representative selection of both real-world and generated graph instances, covering significant application areas as well as interesting classes of graphs.

Visit http://graphdrawing.org/grapharchive/ to see their nascent effort.