I think most would suggest using an automatic version control system like CVS or SVN.
Naming by hand, though, I personally would go with filename_YYYYMMDD or filename_YYYY-MM-DD, ie filename_2006-08-30. That way the files will be properly listed in date order when sorted by name.
I much prefer using month numbers instead of textual abbreviations for the aforementioned sorting purposes. I can 'see' them just fine.