How can I animate my Cycles shaders? For a scene, I have to change shader parameters (using nodes in Cycles) as time goes on in the scene. 

I've looked for a node that inputs a time sweep or frame number, but neither is available in Cycles. Am I looking in the wrong place? Or is there a workaround/trick I don't know about?
You can keyframe any value on the nodes by Right Clicking on the value and then choosing Insert Keyframe. This will set a keyframe on the current frame. 

When you add a keyframe the field will turn yellow to indicate there's a keyframe on that frame. If you move along the timeline, the field will turn green to indicate the field is keyframed, but not on the current frame.