I don't have an IPod or IPhone so I can't say. I only have a laptop. I used to have an IPod though, but I lost it. I didn't use it for anything except music.
Well I have an Android phone so I'm going to go with apps from the Android Market.
Google Goggles is fun, you take a picture of anything and it searches the web for like images. I have an app that lets me use my led flash as a flash light, one that emulates a GBA and I'm looking at buying one that emulates the PSX and an app that let's me turn my phone into a WiFi hotspot.