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.
See the [PhyloPic][1] project.

Edit: and the [rphylopic][2] project to access PhyloPic from R.


  [1]: http://phylopic.org
  [2]: https://github.com/sckott/rphylopic