My wife has worked as translator off and on for most of her life. Her grandparents taught her Sanskrit when she was small, she picked up Vietnamese from her neighbors, learned English from missionaries and studied Japanese in college.
She loves to read, and I'm used to finding notes and Khmer translations of English words and phrases scrawled in the margins of our books. She's always reaching for that clear, nuanced translation of the bedeviling English language.
There are some free, if clunky online Khmer-to-English dictionaries available. There is the exhaustive if inelegant SEAlang Library for Khmer. There are dictionaries for the Mac and PC floating around out on the Internets as well. And we even have a copy or two of various dead tree dictionaries.
Khmer Dictionary for iPhone. It is useful and an easy way to look up general English words — though it is lacking in more specialized fields, like medical terminology. And, as it's on her iPhone, it's always handy.
So now she reads books even faster — and there are no more pencil marks in the margins.
If you're really on the hunt for Khmer apps in iTunes, you should check out Khmer Clock, which does exactly what it promises.
There's also Khmer Keyboard for your Khmer typing needs. It can help teach the proper way to type using Khmer Unicode rather than the outdated Limon font.