I have committed a plugin called "Markup: Include entry data".
This plugin allows you to use HTML-like tags to include portions of other written entries in your current entry, by using this code in your Entries (and by configuration comments, nuggets, ...):
This would show the body and title of Entry #42 in your current entry. Beware you may face caching issues and that markup of those entries may only get parsed if you put this markup plugin before the other markup plugins.
I hope someone can use it. It is a cool shortcut to include the introduction "body" of an entry in your sidebar with a link to the full entry.