Most of you have probably already heard of Ralan.com but for those of you who haven't, this page should become your online bible. Ralan does a really good job of keeping these markets updated with status reports and he even sometimes leaves a little commentary based on either his experiences with a publisher, or those of his readers.
The best thing about Ralan.com is that it's absolutely free. There's no ridiculous fee like you get with writer's market, and Ralan.com is very well organized and easy to navigate. It doesn't have quite the polished look of duotrope.com, but that's another thing that I like about it (once a web page looks too "slick" I start to forget that it was made by a human being...and I HATE robots!).
For those of you who are just starting out, I recommend that you peruse the lists of publications on Ralan and then start following a couple that sound interesting. Generally, I like to follow the philosophy of sending my stuff out to the highest paying publications first and then sending them off to other markets as they get rejected (your work is always going to get rejected a number of times...unless your uncle is the guy running the web page).
Actually I've found that quite a few of the editors on these pages offer some pretty good criticisms in their rejection slips. It's always irritating when you get some sort of dot matrix printed form that doesn't look like a human eye ever even glanced at your work (damn robots), but when you get a rejection letter that includes a few details and character's names and says they'll be willing to publish you with a rewrite...heck...you can't do better than that!
Ralan is a lot of fun, so have at it! Think of this page as your number one resource as an online fiction writer. The only other piece of advice that I can give you is to FOLLOW THE SUBMISSION GUIDELINES TO THE LETTER! If they tell you to paste the story into the body of the email, paste it into the body (don't send an attachment). If they tell you to write the whole story in blue ink...then WRITE it in blue ink! It's just like talking to the cops don't give them an excuse to write you a ticket (or reject your submission). And, amazingly, if you follow the submission guidelines, you're already ahead of half the people who are submitting.