Below are links to some excellent science fiction and speculative fiction magazines from around the world:
Asimov's http://www.asimovs.com/
Analog SF http://www.analogsf.com/
Afterburn SF http://www.afterburnsf.com/
Alien Skin http://www.alienskinmag.com/
Apex Digest http://www.apexdigest.com/
Aphelion http://www.aphelion-webzine.com/
Arcane Twilight http://www.arcanetwilight.com/index2.html
Aeon http://www.aeonmagazine.com/
Andromeda Spaceways http://www.andromedaspaceways.com/
Aurealis http://www.aurealis.com.au/
Alfred Hitchcock http://www.themysteryplace.com/ahmm/
Albedo 1 http://www.albedo1.com/index.html
Alien Q http://www.alienq.com/
Allegory http://www.allegoryezine.com/
Aberrant Dreams http://www.hd-image.com/fiction.htm
Aoife's Kiss http://www.samsdotpublishing.com/aoife/cover.htm
Atomjack http://www.atomjackmagazine.com/
Antipodean SF http://www.antisf.com/
Anotherealm http://anotherealm.com/
Bewildering Stories http://www.bewilderingstories.com/
Beyond Centauri http://samsdotpublishing.com/purchasecenter/magazines.htm
Ballista http://www.mucusart.co.uk/ballista.htm
Borderlands http://www.borderlands.com.au/
Cemetary Dance http://www.cemeterydance.com/
Clarkesworld http://clarkesworldmagazine.com/
Clonepod http://www.clonepod.org/
Cerulean Rain http://ceruleanrain.com/
Chizine http://chizine.com/
Concept Sci-Fi http://www.conceptscifi.com/ezine.htm
Cayote Wild http://www.coyotewildmag.com/
Dark Wisdom http://www.darkwisdom.com/
Dark Energy http://www.darkenergysf.com/
Darwin's Evolutions http://www.darwinsevolutions.com/index.html
Drabblecast http://web.mac.com/normsherman/Site/Podcast/Podcast.html
Doorways http://doorwayspublications.com/whoweare.htm
East of the Web http://www.eastoftheweb.com/short-stories/
Electric Spec http://www.electricspec.com/
Escape Velocity http://www.escapevelocitymagazine.com/
Expressions http://www.samsdotpublishing.com/expressions.htm
Fantasy & Science Fiction http://www.sfsite.com/fsf/
Future Fire http://futurefire.net/
Fusion Fragment http://www.apodispublishing.com/fusion/index.html
Futurismic http://www.futurismic.com/
Fictitious Force http://www.sciffy.com/dnn/
Fifth Dimension http://samsdotpublishing.com/fifth/cover.htm
Flash Fiction Online http://www.flashfictiononline.com/
Flashquake http://www.flashquake.org/index.html
GUD http://www.gudmagazine.com/
Glimmer Train http://www.glimmertrain.com/
Heliotrope http://www.heliotropemag.com/
Ideomancer http://www.ideomancer.com/main/ideoMain.htm
Interzone http://ttapress.com/category/interzone/
Jim Baen's Universe http://www.baens-universe.com/
Midnight Street http://www.midnightstreet.co.uk/
Morpheus Tales http://www.morpheustales.com/index.htm
Neo-opsis http://www.neo-opsis.ca/
Night Train http://www.nighttrainmagazine.com/
NFV Magazine http://www.freewebs.com/nvstuff/index.htm
Orson Scott Card's Intergalactic http://www.intergalacticmedicineshow.com/
OG's Speculative Fiction http://theopinionguy.com/page2.html
Pedestal http://www.thepedestalmagazine.com/
Pantechnicon http://www.pantechnicon.net/
Planet Magazine http://www.planetmagazine.com/
Postcards From http://postcardtales.blogspot.com/
Reflection's Edge http://www.reflectionsedge.com/
Revolution SF http://revolutionsf.com/
Lone Star Stories http://literary.erictmarin.com/index.htm
Skive http://www.skivemagazine.com/
skiveflash http://skiveflash.mobi/
Strange Horizons http://www.strangehorizons.com/
Short Fiction World http://shortfictionworld.com/Content_Mgr/index.php?option=com_frontpage&Itemid=1
Sinister Tales http://darknessproductions.com/writing.htm
Silverthought http://www.silverthought.com/
Space Squid http://www.spacesquid.com/
Tales of the Talisman http://www.talesofthetalisman.com/
Tales of the Moonlit Path http://www.moonlit-path.com/
ThrillerUK http://www.thrilleruk.fsnet.co.uk/latest.htm
Triangulation http://www.parsecink.org/triangulation/2007/
The Town Drunk http://www.thetowndrunk.org/contents.aspx
Transmitter http://www.illusiontv.com/transmitter/
Weird Tales http://www.weirdtales.net/
Worlds of Wonder http://www.lilleypress.com/wow/
Wrong World http://www.wrongworld.com/shop/cart.php
Xenith http://www.xenith.net/
Below is a list of some excellent science fact magazines:
Scientific American http://www.sciam.com/
Science http://www.sciencemag.org/
21st Century Science http://www.21stcenturysciencetech.com/
Discover http://discovermagazine.com/
New Scientist http://www.newscientist.com/home.ns
Nature http://www.nature.com/index.html
Nature Physics http://www.nature.com/nphys/index.html
Smithsonian http://www.smithsonianmag.com/
Popular Science http://www.popsci.com/
Popular Mechanics http://www.popularmechanics.com/
Cosmos http://www.cosmosmagazine.com/?gclid=CJC-w7iKgokCFRh3YAodWxVwQQ