Answer:
My love, when I gaze on thy beautiful face. Careering along, yet always in place, the thought has often come into my mind. If I ever shall see thy glorious behind.
Two horses, swiftest traveling, harnessed in a pair, and grazing ever in places. Distant from them.
Always old, sometimes new. Never sad, sometimes blue. Never empty, sometimes full. Never pushes, always pulls.
The itsy bitsy teeny weeny yellow polka dot variety is quite popular.
I am the tool, for inspiring many. Buy me in the store, for not much more than a penny. Don't overuse me, or my usefulness will go.
What never gets any wetter no matter how hard it rains?