I recently ran into a couple of situations where I wished I could have stopped comments on my blogs without having to lose any of the other settings. A recent comment flood attempt comes to mind.
Dougal came up with the wonderful Spammer Tar Pit plugin to temporarily stop the floods and that plugin gave me some ideas that I put together into another set of plugins.
The "Stop Comments" plugin temporarily turns off comments for your whole blog without affecting individual settings for each of the posts. In other words, if at some time you want to stop people from commenting on your blog for a certain period of time, simply activate this plugin and all comments are dropped with a polite message. Once you are ready to turn them on again, simply deactivate this plugin and you are done.
The "Take Down Blog" plugin is a one liner. If for some reason you want to prevent people from reaching your blog, just activate this plugin and your readers will get a polite message asking them to come back soon and nothing else. This could be further refined with html pages and such.
Both these plugins can be downloaded here. Installation is as simple as copying the contents of the zip file to your wp-content/plugins directory.
Please leave comments and feedback.