These are the 3 magazines that I like, where Science Fiction and/or Fantasy genres are concerned. By "magazines", I mean there's stories and stuff, not entertainment news. Actually, they're pretty much it for SciFi and Fantasy serials - at least in NLB public libraries. Not many of such magazines around.
The magazines are great companions when going on long trips (like on a plane). The stories are short enough so that you don't get bored with just one story; they are compact in size; they don't just contain stories - all 3 magazines have reviews (of new writers, books, websites) which is a great source of further reading list for Sci Fi/ Fantasy fans.
Asimov's Science Fiction - I'd recommend this for readers who like the Year's Best SciFi series and/ or the Mammoth book of Science Fiction series. Stories from Asimov's frequently make it to those series, but it could be that Gardner Dozois was the editor in all three (Dozois stepped down recently though). I can't quite say why I prefer stories from Asimovs than Analog... the stories in 'tend to be more contemplative perhaps.
Website - www.asimovs.com
They have a searchable index of everything that has appeared in Asimov's.
Analog Science Fiction & Fact - I love the thought-provoking editorials by Stanley Schmidt. On the whole, the "flavour" of Analog is different from Asimov's, even though they have SciFi stories. It has regular columns on science facts - speculative but rooted in real cutting-edge science - on topics like Space Exploration, Nuclear Science, Bio-tech, Nano-tech etc.
Website - www.analogsf.com
They also have a searchable index.
The Magazine of Fantasy & Science Fiction - From the website:
... founded in 1949, is the award-winning SF magazine which is the original publisher of SF classics like Stephen King's Dark Tower, Daniel Keyes's Flowers for Algernon, and Walter M. Miller's A Canticle for Leibowitz. BTW, read "Flowers for Algernon" if you have not done so.
As implied from the title, the stories are more skewed towards Fantasy. Its SciFi stories are perhaps less of the 'Hard Science' type compared with, say, Analog.
Website - www.sfsite.com