Google Code Search has been incredibly valuable to me as a developer - I use it a couple times a week to see how other developers have used (usually poorly documented) APIs. It's also convenient to see the internals of some of those APIs, or to find which API corresponds to the functionality you want (it's a great resource for Android in particular -- give it some of the text you see on screen, and it'll usually find the implementing class).
Now that Google shutting down code search as of January 15, 2012, are there any good replacements?
Take a look at these: