Is there any built-in, add-in solution for visual studio to compare two files and display result with differences? I could\'t find one...
Once you add some version control plugin to visual studio, you can select the tool for diff.
Perforce are giving away their diff and merge tool for free, it is very good and you don't have to be using the perforce version control system to be using it. one can download it from their site; it is called p4merge. when running the installer you should only select the feature "Visual Merge Tool (P4Merge)" and unselect the other features which are only relevant if you are using perforce.
personally I use vim because it do syntax coloring (which I feel is very helpful especially when you do diff or merge) but it has a steep learning curve.