Is there a command or plugin that I can use to show all the lines I have edited in a Vim session? I would like to be able to have all the changes I have made highlighted when working in co-workers projects and lost in lines of code.
The changesPlugin seems to work just fine for this type of thing.
Once installed, just run
:EC after making changes to a file.
I would suggest using a revision control system, such as CVS, Mercurial or Subversion (etc.). These all come with the ability to compare the working copy of a file with whatever was last checked into the repository by you or your co-workers.