Register & Read includes approximately 1,200 journals from more than 700 publishers, a subset of the content in JSTOR. This includes content from the first volume and issue published for these journals through a recent year (generally 3-5 years ago). Free read-online access (must register for a myJSTOR account).
The Merit Software Repository contains interesting software developed at Merit Network in Ann Arbor, MI. Most of it is open source and available for download. Each project has its own page or pages and can be accessed via the above tabs.
Last week the free and open access repository for scientific (mainly physics but also math, computer sciences...) papers arXiv got past 500,000 different papers, not counting older versions of the same article. Especially for physicists, it is the number-one resource for the latest scientific results. Most researchers publish their papers on arXiv before they are published in a 'normal' journal. A famous example is Grisha Perelman, who published his award-winning paper exclusively on arXiv.