There are an assortment of such things out there. Some are available in ebook format, and others are intended for reading on line. Free unless indicated:
Aeon SF magazine. Short fiction and articles, for sale at Fictionwise
http://www.aeonmagazine.com/index.html
FLURB - online webzine of "Astonishing Tales", edited by Rudy Rucker
http://www.flurb.net/
Hub SF - weekly UK SF periodical, available in PDF and Mobipocket format
http://www.hub-mag.co.uk/
Internet Review of SF - news and commentary
http://www.irosf.com/
Infinity Plus - UK online SF and articles site
http://www.infinityplus.co.uk/
Strange Horizons - weekly UK online SF periodical
http://www.strangehorizons.com/index.shtml
There are doubtless more. The above are simply links close to hand.
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Dennis