Here are the things I use regularly that iOS doesn't/probably-will-never have.
- Free turn by turn navigation that's better than any dedicated gps device.
- Wifi or bluetooth tethering. I recently was travelling with my girlfriend, and we both could access the internet on our laptops routed over WiFi through my phone. The hotel even had free wifi, but it was easier to not bother with figuring out how to set that up, and just use my phone.
- Fully integrated Google Voice.