EditPad Lite has a nice feature (CTRL-E, CTRL-I) which inserts a time stamp e.g. \"2008-09-11 10:34:53\" into your code.
:r! date
You can then add format to the date command (man date) if you want the exact same format and add this as a vim alias as well
:r! date +"\%Y-\%m-\%d \%H:\%M:\%S"
That produces the format you showed in your example (date in the shell does not use \%, but just %, vim replaces % by the name of the current file, so you need to escape it).
You can add a map in your .vimrc for it to put the command automatically, for instance, each time you press F3:
:map :r! date +"\%Y-\%m-\%d \%H:\%M:\%S"
(Edited the from above :) ) (Edit: change text part to code, so that
can be displayed)