While not open journals per se, many (new) papers will typically be available at academic homepages (preprints), via "All [X] versions"-links in a google scholar [0] search, or on arXiv [1], depending on the subfield.

For instance, the machine learning group (Yoshua Bengio, Ian Goodfellow, et al.) at the University of Montreal (the people behind open source software like Theano [2], Pylearn 2 [3], etc.) regularly makes papers available on arXiv, and is currently working on a book about Deep Learning, drafts of which are freely available [4].

[0]: http://scholar.google.com [1]: http://arxiv.org [2]: https://github.com/Theano/Theano [3]: https://github.com/lisa-lab/pylearn2 [4: http://www.deeplearningbook.org

I'm not familiar with the names of the particular CS journals as that's not my research area, but it's relatively easy to find the type of journals you're looking for. Just search for "open access computer science" and you'll find plenty of journals with free access to articles.