Put this in the "weird" box, but we've found that the HTC Legend, the new Android powered handset from HTC, can also double as a stylus for the iPhone.
As you probably know, capacitive screens like those on the iPhone or Google Nexus One can, on the whole, only be operated by interrupting the electrical field of the touchscreen with another, ie a finger or a sausage, but there are a couple of styli which work because they're conductive.
It turns out, the HTC Legend thanks to its aluminium sleeve, works too.
You have to hold it just right and it's not flawless, but it is kind of fun.
Of course you have to ask yourself why you would want one phone to double as a stylus for another, but hey I'm sure you can think of a reason.