In IDEA, we can comment/uncomment lines in java as well as html,jsp, xml files with the same keyboard shortcut combination. I tried doing that in eclipse but was not able to
I use Shift+Ctrl+/ to Add Block Comment in both XML and JSP files (works at the line level or for a selected block).
Just in case, if you are looking for a particular shortcut, you can use Shift+Ctrl+L to Show Key Assist (i.e. the Commands and their Bindings).