What is the easiest way to figure out who wrote/edited this line of code?

That looks like the blame function, supported in eclipse with CVS, or with Subversion (also in eclipse)

As you mention, the eclipse-name for that feature is Show Annotations.

You don't mention wich source control are you using.

If you're using Subversion, you can take a look at:

svn blame

:)

For Visual Studio .NET with TFS.

The function is "Annotate" and works pretty much the same with Blame.

(personally I refer to these as the team's witch hunt tool).