I tested attachment_doc plugin - it work well for .DOC and .PDF
attachments, but not support new OpenOffice.org OpenDocument format
(ODF) (content-type probably application/vnd.oasis.opendocument.text),
only old .SXW format.
Extending with this functionality would be fine (e.g. with external
program o3tohtml from o3read package, http://siag.nu/o3read/, which
is capable convert both text and spreadsheet documents).
And what about new M$ Office Open XML support?