I was recently talking to a few fellow librarians on the Open Access initiatives particularly focused on the Sciences. I’ve collected a few that I am currently aware about.

SCOAP3
A consortium facilitates Open Access publishing in High Energy Physics by re-directing subscription money. The initiative proposes a new business model for scientific publishing, with the goal of extending open-access to the bulk of peer-reviewed particle physics literature. An international consortium of funding agencies, libraries and research institutions aims to convert prestigious peer-reviewed journals to open access in a way transparent to authors, at the same time being open for any new high-quality particle physics journal. Publication costs will be centrally borne by the consortium and will be shared according to the respective number of journal articles of its member countries.

ArXiv.org
An Open Access archive of 496,504 (and growing!) electronic preprints in physics, mathematics, computer science, and non-linear sciences.

Scientific Commons
Currently indexing 13 million items, the Scientific Commons aims to provide the world’s largest communication medium for scientific knowledge freely accessible to the public. This service harvests information from a range of open access scientific repositories. Content includes hard sciences as well as the humanities.

Scirus
With over 450 million scientific items indexed at last count, Scirus  allows researchers to search for not only journal content but also scientists’ homepages, courseware, pre-print server material, patents and institutional repository and website information.