Fuel Prices
Up on the appstore at the moment, and it's free, called Pumps.ie, shows you the cheapest fuel in your area based on your location, and if your phone supports it, it'll show you a map of how to get there.
Dyno
Dynolicious, uses the accelerometer in your phone, and stats on your vehicle (Weight, etc) to calculate bhp, and will give you dyno graphs to save. It's been compared with a real dyno on youtube, and it's pretty accurate. It's €10.49.
Maintenance
Haynes have created an app for basic maintenance, with tips, and videos on how to perform the simpler to intermediatery tasks. It's called Haynes Car Tips, and is 3.99 - not the worst.