Clear for iPhone has always been a visually stunning to-do-list app. The latest version's eye candy has been tweaked, but it's also made the jump to the iPad's larger screen. Add "Check out Clear" to your to-do list.
Google Field Trip is designed to help you explore unchartered territory, but it's definitely not perfect.
The next major version of iOS will allow Bluetooth accessories to use Notification Center and make it easier to run Bluetooth-enabled apps in the background.