I have a Canon S100 and am generally quite pleased with it. I am discovering, however, that more often than not I am wanting a much better zoom lens for bird and wildlife shots. I am thinking of going with a Canon SX50 HS with its 50x optical zoom or something similar costing no more than $500.
In short, I want a camera with a much better optical zoom, one which would complement what is lacking in the S100, so used together, I am well equipped to cover off most applications.
The sx50 is a fine choice - as you are already familiar with Canon camera interface. I use the canon sx40HS it's 35x zoom is great for wildlife. But under good light conditions. When there is low light the camera's autofocus is not the best performing. According to canon they have improved the autofocus speeds of the sx50Hs considerably when compared to the sx40.
You can also check Lumix FZ 150 (this has very fast AF), Sony HX100v ( has sweep panorama) and nikon P510 & P500.