Google has set up a new search enginge specifically for source code: /* Code Search */. Important difference with their normal search engine is that it allows restricting your search by programming language, license and filename and package. I have not been able to figure out how to use 'package' yet, but the others are pretty clear. For example: AtomContainer license:LGPL lang:java should do it. The search results show filenames, licenses and programming languages:
Alternatively, you can use Koders, which is a source code search engine too. It has been around for quite some time now, and shows the copyright notice too. Additionally, Koders offers a plugin for Eclipse which adds a search 'view' which will show the HTML from the website in an editor window inside Eclipse.