Mike
You have a sphinx caterpillar. They have a tail on the rear end...not sure about any spike on the head??
What was it feeding on?
There are many sphinx caterpillars that feed on many things. Yours kind of looks like one that feeds on tomatoes, but without more photos from other angles like a side view, it can not be ID'ed further.
Here are images of a few of this family of caterpillars - http://bugguide.net/node/view/193/bgimage
