Is there any resource of standardized and uniformly stylized (and potentially, but not necessarily, even free) icons of popular model organisms (including E. coli and other popular unicellular organisms)? 

I wish to use it for making a small tabular-like panel with ~10 organisms, next to the main figure panel, which would show the detailed data for one organism.

Some model organisms are not yet included in unicode.
We use the EMBL-[EBI Framework][1] font icons for representing the species in our gene trees. To see the ones we have used, go to our page showing a profile of the [PTEN][2] drug target and expand the 'Gene tree' tab (second from the bottom).


  [1]: http://www.ebi.ac.uk/web_guidelines/EBI-Icon-fonts/v1.1/
  [2]: http://targetvalidation.org/target/ENSG00000171862