There's a lot of unit converter apps in the App Store: it seems like it's one of the latest trends of 2009.
Anyway, I stumbled upon this app, Measures, and I thought "wow,just another one". But, after some weeks of testing I must admit that it works and - most of all - it's really easy to use.
Using Measures is simple: you choose a category, pick up the units you want, tap the numbers and convert.
Easy and well done. The calculator is accessed by tapping the display once. To access the settings menu, tap the small 'i' button in the right-top corner of the display.
Moreover, you can also change the app appearance. See the screenshot below:
Other features include daily updated currency exchange rates and a ton of categories to choose from.