Smaller publications, especially online pubs, tend not to offer a formal contract when they buy your work. If the editor doesn't specify what rights he or she is buying, be sure to confirm this information with them. Some new writers tend to hesitate about this because they're afraid of antagonizing the editor or losing the sale. DON'T HESITATE. It's in both your interest and the editor's to know what rights you are selling.
Here are some useful online resources:
Basic Copyright Concepts For Writers by Clair E. White, from Writers Write. This article explains what copyright law covers, how to copyright protection, registering a copyright, how long copyright lasts, and copyright infringement. The author is an attorney with over ten years' experience in law firms.
Warnings and Cautions for Writers - Copyright, part of SFWA.org. Covers copyright basics, the question of whether to register or not, registration services, and copyright myths. One common myth, for example, is "poor man's copyright"...mailing yourself a copy of your work and retaining the envelope unopened. This article points out that this would be easy to fake: someone mailing themselves an empty envelope, and then stuffing it later. This does not provide legal protection in countries where official registration is a prerequisite for filing an infringement suit. Has a useful list of links at the bottom of the page.
Understanding Rights and Copyright by Moira Allen, from Writing-World.com. Addresses the concern from some newbie rights that editors will steal their ideas, various types of rights, how to protect yourself. Moira also has a great list of articles related to copyright information on her site, as well as copyright info links.
10 Big Myths about copyright explained by Brad Templeton is "an attempt to answer common myths about copyright seen on the net and cover issues related to copyright and USENET/Internet publication."
U.S. Copyright Office: Lots of info here, including copyright basics and how to register a work. Please note that the new basic registration fee went up on July 1st to $45.
Canadian Intellectual Property Office: Copyright info from a Canadian perspective.
Intellectual Property (UK): Government-backed, this is the home of UK Intellectual Property online. Covers copyright, designs, patents and trademarks. There doesn't seem to be an official way to register copyright in the UK.
Do you know of other useful copyright info sources? Any useful tips for writers on how to avoid being snagged by copyright confusion? Please do post them below.