Love all lambda functions from c#, oh and extension methods. They make life way easier in c#.

From PHP: file_get_contents/file_put_contents. It does a simple job but allows many-many sources and protocols (like HTTP) to be used as sources.

Other than that - monkey patching in Ruby, wish every language had that, because there are a lot of closed-for-extension scripts out there, and when you need to override a specific thing in the code you cant.