How to get the last commit date for a bunch of files in Git?

The following command will be helpful:

git log -1 --format=%cd filename.txt

This will print the latest change date for one file. The -1 shows one log entry (the most recent), and --format=%cd shows the commit date. See the documentation for git-log for a full description of the options.

You should be able to easily extend this for a group of files.