I found a bug on a particular line, and need to track down the history for that line. This is easy enough with git blame, but in this case I'm getting false positives. There was a previous check-in that changed whitespace on that line. Obviously that was not the commit that introduced the bug.

Using git log with the -L flag you can specify a file and and range of lines to search through.

git log -L 57,57:index.php

This will show all the commits in index.php where there was a change on line #57.

See also: Finding commits that match a search term