I did a little looking and according to
Ethanol Producers Magazine, "... nonmetallic materials like reinforced fiberglass, Buna-N, Neoprene rubber, polypropylene, nitrile rubber, Viton and Teflon meeting acceptable usage standards with E85."
Some of those materials are not really appropriate for use in this application, (eg, Teflon and polypropylene tend to cold-flow). L33T Z34's recommendation for Viton sounds like a good one. I saw some reports that BMW had problems with Buna-N o-rings.
Kalrez scores high on EtOh, gasoline, and high-temp scales but I don't know if the other properties would be appropriate for use on injectors.