One would think, based upon Apple's unrelenting scoffing regarding a stylus, that they'd never put one out. Looking at Apple patents, though, tells another story.
Most recently a patent for a graphics tablet addressing the particulars of a screen designed for finger touch interfacing being used by a stylus was posted on Patently Apple.
The basic premise is that in order to have a stylus that works with existing capacitive-touch tablets, you need a pen large enough to not slip between the "cracks" in the sensors. Capacitive elements can be relatively low-density because of the size of a typical human finger--much larger than a common pen or stylus. The best method it seems is to have a disk at the end of the pen on a pivot to make sure a capacitive sensor is being hit.
Sensors determine the center of the disk based on the partial "print" the disk is leaving on a capacitive sensor, and this input is sent to the device for use in tracking user input. The science of it is actually pretty cool when you get into the nuts and bolts, and a lot more complicated than I expected it to be.
Visit Patently Apple for patent sketches and more info.
Keep in mind that this is just a patent and may or may not make its way into future products. That said, it looks interesting, but also seems awkward. I've used touch-style pens on the iPad that don't have a disk attached to the end and they appear to work fine, do you think this is something that is absolutely necessary?