I've always included a certain number of links to useful websites with tools for writers over in the sidebar. The link list has grown substantially, though, and the resources have become lost. So I've created a separate box for resources (lists of agents, lists of markets, a postage calculator) and eventually I'll move all the relevant links into it.
The occasion for the new box is that I just learned (thanks, Ellen!) about LitMatch.net a site that lists literary agents and more. It's free to register and if it turns out to be useful I'll have more to say. At first glance (too soon to be definitive) it appears to be an improvement over AgentQuery.com, which is already pretty amazing as a free source of information. For now, I'll refer to both.
If you know of other useful resources, please leave a comment and I'll add them to the Writers' Resources link list.