Compile&Run in over 50 langs from Ada to Whitespace without downloads.
ideone.com
ideone.com
I've only really seen services like this (specifically, most popularly, http://codepad.org) used to demonstrate test cases when people are asking for help with their code. The "IDEdroid" app listed on ideone's API page (http://ideone.com/api) looks interesting though, but yet again, it is an only marginally useful application.
But I can not agree with marginality. First, the situation when people are asking for help is quite common. Second, there are more cases when such services might be useful: experimenting with a new language, comparing/demonstrating the behaviour of a particular compiler, sharing groups of pastes (lecture examples?), and more.