The plot below shows the biological sub-disciplines leading in the area of open access publishing (click on the plot for readable x-axis labels):
Bioinformatics has by far the largest amount of “open access” chatter. In purple you can see the relatively flat distribution of “journal” as a control. As a bioinformaticist myself this seems to make sense, as the leading figures in the open access movement come from this field. However, other communities (physics, computer science) have been operating an informal open access model for a lot longer (preprint servers and/or widespread preprint availability).