Despite of the usual convention of using ctrl+/, I found ctrl+shift+c is actually the way to go if you want it to work on everything.

I care mostly about being able to toggle comment in the following file types:

• source code – comment with // or /* and */ block
• markup e.g. xml/html – comment with <!– and –> block
• property file value – comment with #

The following behaviors are tested in Eclipse version 3.6.

• ctrl+/
  • source code: Toggles //
  • markup: No affect
  • property file value: Toggles #
• ctrl+shift+/
  • source code: Only add but does not remove /* and */
  • markup: Only add but does not remove <!– and –>
  • property file value: No affect
• ctrl+shift+c
  • source code: Toggles //
  • markup: Toggles <!– and –>
  • property file value: Toggles #