This patent application from Apple is for an application called Podmap. It looks like it has everything that is needed to build a GPS application that the one found in in-car navigation systems. Of course, this could be used to turn an iPod Touch or an iPhone into a fully-featured GPS navigation system or it could be used to build a stand-alone device, an iGPS, if you want.
Turning existing devices into better navigation devices would make more sense in the short term. After all, we believe that the iPhone 2 will have a GPS chip and a 3G connection, which would be required to access the network described above. However, a stand-along GPS device that has a 4.3” to 7” display is not completely out of the question.
Note that this is “just” a patent application. It does not mean that Apple is actually working on it, but at least, they are “thinking” about it.