This is a very interesting question. I have seen many pictures of John Dillinger himself, but very few of the men who were his "gang." I did a quick search and found a few sites you should take a look at. I've posted the links to those sites in the sources section.
The first site, jhdillinger.fortunecity, is a scrapbook of Dillinger and includes a section devoted to his gang. According to that site, the men who helped Dillinger commit his crimes were Harry Pierpont, Charles Makley, Russell Clark, John Hamilton, Homer van Meter, Harry Copeland, Baby Face Nelson, Tommy Carroll, Eddie Greene, and William Shaw. The site has photos of the first four men on that list.
You might also want to check out the FBI's web page on Dillinger. I've posted that link as well.
Dillingerswomen.com is devoted to the wives and girlfriends of Dillinger and his men. You might find that site interesting.
I hope this helps you!