No 404 Errors
When I installed my first WordPress site I noticed that strange things happened when someone mis-spelt the url of a page. After extensive debugging the technicians confirmed that the WordPress 404 handler was incompatible with the shared hosting. After reviewing several exixting plugins I decided to modify one of them and release it myself. The result is No 404 Errors.
This plugin adds a settings page where you specify the page number that 404 errors will be redirected to. To find the page number simply hover over the edit link on the list of pages page on the dashboard. The main plugin then intercepts 404 errors, redirects the browser to this page and assigns a 301 code.
The only minor complication is that your error page will appear in the output of the wp_list_pages function. The solution is to add the page number to the exclude parameter wherever that function is called.
The plugin can be downloaded from http://wordpress.org/extend/plugins/no-404-errors/.