After running into problems with installing a plugin and not knowning how to debug the plugin system, I decided to familiarize myself with the plugin API. Below are the two simple plugins I wrote to do this, but that others may find useful. As far as I know, these features aren't offered by other plugins, but even if they are, it was still a good learning experience
Random Entries is a sidebar plugin that will display a configurable number of random entries with configurable min and max ages. It was inspired by the History plugin.
Edit Link is an event plugin that appends an Edit option to entries in extended view. It is based on the Delete Link plugin.
The plugins can be found at http://brett.narnarnar.com/s9y_devel/, with examples at my blog. To install, just download and unzip them inside your plugin/ dir, then configure them through the admin interface.
Let me know if they work for anyone besides me!