How "hard" and engineering-focused do you like your SF? Analog etc are generally considered the flagship of that type of SF. I like my SF a bit (or a lot) more diverse than that, so maybe take that into account.
Clarkesworld and Lightspeed are great. I have also supported (but not yet read) Uncanny and Crossed Genres. Check out Strange Horizons, Apex and Tor too.
http://clarkesworldmagazine.com/
http://www.lightspeedmagazine.com/
http://uncannymag.com/
http://crossedgenres.com/