Although it is not yet men­tioned on the ‘New fea­tures’ page, Google have added a ‘report phish­ing’ link to gmail. It’s under the more options link when view­ing an email.
I for­got to men­tion a while ago that they star­ted mark­ing emails with from addresses at gmail.com, but which were not sent through gmail with the following.

Warn­ing: This mes­sage may not be from whom it claims to be. Beware of fol­low­ing any links in it or of provid­ing the sender with any per­sonal information.

And then they don’t make all the links in the email click­able any­way!
Unfor­tu­nately, this one is applied too rig­or­ously for me, or at least the rules are too simple minded. For exampe, any­thing on a mail­ing list from someone with a gmail account gets flagged thus.