I'll echo akamaka -- I like your graphs far more than timf's flash-based ones.

You might like to consider adding some indication (dotted lines, perhaps) of what the hourly rate for reserved instances is, since this should be approximately a floor on the hourly spot rate.

EDIT: Also, please adjust the vertical scaling based on the set of instances shown -- if I'm only looking at the price history for m1.small, it's silly to have it squished into the bottom 5% of the graph.

Suggestion -- use small multiples showing the data center prices on one screen, probably by making the graphs 1/4 size. Place your explanation in the space left empty since there's only (currently) 3 centers.

"A small multiple design consists of a single design repeated several times within the eyespan, each example showing a different value of the independent variable(s)."

hey casey, nice visualization. makes the relative prices of different instance types very clear.

I like your style of graphs.

ok, i've added windows ... now it's your turn again ;)