I made two new MediaWiki extensions.
1) Poem Extension. A very simple extension, which only adds a line break at the end of each line between <poem></poem> tags, which can be truly useful for, err, poems. Its page is at http://meta.wikimedia.org/wiki/Poem_Extension
2) ShowHide Extension. A bit more complex extension, which enables you to make a portion of wiki page which could be shown or hidden, as ToC could be now. Its page is at http://meta.wikimedia.org/wiki/ShowHide_Extension
Please tell me what do you think of them :)