I really like krzat's contribution. I suppose I've associated SFML with an ellipse for a too long time
With new colorscheme, lighting and drop shadow:
Here some integration tests based on his logo:
With Cornstalk's font:
I like the idea of the acronym "SFML" being a part of the logo itself, I think the logo will be more identifiable that way.
While I also like the concept of a pentagon/power button, a multimedia library is something too much abstract to be easily represented by just a pictograph, and it's hard to have a distinctive visual representation.
[attachment deleted by admin]