I guess it would be nice to have something to not just
match but even
beat the iPhone, otherwise it's just going to sound whiney: "oh, but I have that
too".
It seems that the frame rate (on my Galaxy) is considerably lower than the iPhone, so you might wanna stay away from games. I don't know if this is specific to the Galaxy, or if Android is just more lax about screen updates

but it's definitely affecting even the simplest of games (like
Friction Mobile).
I'd show off some of the things that the iPhone can't do -- such as the
widgets (plenty of things to choose from there),
changing to a different Input Method (different keyboard layout, or perhaps the handwriting one). (But that would expose you to jabs about how crummy text selection is in Android.

) You could also
record a new ring tone (with, say, Droid Record & Ringdroid) -- I don't think the iPhone will let you do that?
Show off multitasking by simultaneously syncing your email, playing a podcast, and surfing in a couple of browser windows. Or simply change the background to a photo you just took!
If you have a Galaxy, you can always blind

your audience with
Glowing Pear! Seriously, a certain kind of banal apps are always going to impress people beyond any reason: flatulence, guns, and other sound boards; light saber apps (hey, you could have a phone-on-phone duel!), and other fun doodads.