What are your favourite online writing and reading resources?

We have a large selection of links that we hope writers and readers will enjoy. You'll see most of them (sorted alphabetically) in the left panel here, under "Recommended," and a sorted list on our site.
Do tell us what you think of the selection.
If you have some links of your own to recommend, even better. Either mail them in, or leave a comment here, with the URL and why you think that site is a useful addition. (Note to the Contributors: perhaps you can post reviews of the sites you find most useful? Feel free to pick up one of the existing links, or choose one of your own.)