These are links I've found useful or interesting.

The magazine about spec-fic: The Internet Review of Science Fiction (IROSF)
A useful forum for writers:  Absolutewrite.com
The well-known market trackers and other useful things sites: Ralan.com and Duotrope.com
Of course there's the online critique group, Critters that is open to all writers of spec-fic.
A Clarion Writers' forum set up in 2009 is open to all alumni and current students of Clarion, Clarion West, and Clarion South, and to current and former Clarion (and CW and CS) instructors. You have to join to participate.

I really like online speculative fiction magazines. They're mostly run by people who are excited about them, and perhaps because they tend to have low overheads, many of them are really innovative. (I estimate that the cost of running an online magazine is about 10% of the cost of a print magazine.) Many of them archive material (with the author's permission), so you can go back and browse. And of course, you can send links to people who you know would just love that story or poem or artwork. Many of them are free, supported by donations or grants.

This is an ongoing list, in no particular order, of some of the electronic spec-fic magazines.

FREE MAGAZINES

• Strange Horizons carries a new story and a new poem each week. In addition, it has art, reviews, and columns.
  

• Expanded Horizons is a new webzine, aiming to push spec-fic out of its comfort zone with more diverse perspectives.
  

• Ideomancer is a quarterly, carrying typically three stories, three poems, reviews and an interview.
  

• Fantasy Magazine is a weekly speculative magazine that carries reviews, articles, and fiction.

• Clarkesworld, also a monthly, is perhaps the opposite, publishing stories that are often dark and disturbing - and memorable

• Heliotrope, a quarterly, publishes short stories, poetry, and articles.
  

• Ruthless Peoples Magazine, a new monthly online magazine based in the UK, available as a free downloadable PDF

• Goblin Fruit is a fantastical poetry magazine published quarterly. It has audio recordings of some poems, read by the poets.
  

• Big Pulp, a new webzine that plans to add new stories each week in a variety of genres: Romance, mystery, horror, adventure, and of course fantasy and science fiction. It also has reviews of books and manga.
  

• Lucrezia is an erotic webzine with a feminist slant and a sense of fun. It's published monthly, but updated during the month with art, stories and articles.
  

CLOSED MAGAZINES

Some of these are leaving their archives up, so the old stories are still available.

• Atomjack closed down end 2009. It was bimonthly, science fiction and science fantasy. Not sure if they'll leave the stories up.
  

• Lone Star Stories has closed down. Its editor, Eric Marin, decided to move on. But the website remains and you can browse for stories.

• Town Drunk also closed in 2009. It was a monthly, with a light-hearted touch, publishing stories that were fun to read.

PAID SUBSCRIPTION MAGAZINES

• Andromeda Spaceways Inflight Magazine is an Australian magazine publishing six issues annually. It contains some excellent humor but isn't limited to light pieces. It's not strictly an e-zine; but it has a PDF subscription option at $20 per year. (The print subscription is higher, especially if you don't live in Australia.)

• Shimmer magazine, a quarterly, is available as a download. The electronic edition is available for $14 per year (or $4 for a single issue).

• Jim Baen's Universe is published six times a year, and costs $30 per year ($6 for only the current issue). Unfortunately, as of April 2010, it's gone - after four years of publication.