The basic idea here is that you can easily link to the wikipedia entry for a given topic by putting the [wikipedia]topic[/wikipedia] tag into your post. The tag is replaced by a link that executes the wikipedia search form for that topic.
The plan is to augment this with a mouseover popup containing an excerpt from the wikipedia page.

Wp-Wikipedia-Excerpt

This plugin replaces [wikipedia]topic[/wikipedia] with a wikipedia search link for that term.

jondor

Add wikipedia extracts to your page as a widgid, above or under your content or using shortcode’s wherever you like.
To connect a wikipedia title and extact to your post, there’s a widget on the post edit page with 3 tabs. 
The first, default, tab just tells you to start typing in the inputfield above. A datalist with finds will show 
up when you stop typing for a few seconds.
When used with geo2wp, on of my other plugins, or with any other plugin which adds coordinates to a post, a second 
Geo tab will be available. Select it and a list of found objects, sorted by distance from the location, will be shown.
The third tab will give you a preview of the found wikipedia info.
Make your pick and update.
Once a wikipedia page is linked to the post, there are also a number of ways to show the info on your site:
First you can add a widget which is only shown when there’s something to show. 
Then you can turn on the switch in the settings for adding the information as a blockquote above or 
below the content.
And lastly there’s a shortcode [wiki] with four options:
[wiki] or [wiki part=extract] to show the extract 
[wiki part=title] to show only the title 
[wiki part=url] to show the ‘raw” url which refers to the wikipedia page 
[wiki part=link] to show a full <a href="" rel="nofollow ugc"></a> with the relevant info filled.
geo2wp has a switch to enable the use of shortcodes in widgets so hack away.
Warning: 
 At this moment all the actions and urls are based on the language selected in the settingsscreen. This language 
 is by default the language of the site at the time of activating the plugin. If you change the language on a later 
 time, it is very possible that the urls to wikipedia will no longer work as the titles will be different. 
 For now I’m pondering two solutions: To store the used language in the wikiData so the language is always know, OR, 
 to make the wikiData language depending. When you select an other language, everything will be gone, but when your 
 go back it will be there again. Opinions are welcome..
As for the other settings in the settingsscreen:
Max. results: The maximal number of results to give back when searching 
Max. search radius: The radius in meters in where to search geographical
Add the wikipedia info to the content: none | top | below 
 Where to show the wikiData blockquote in the content. Default is none.
The jQuery-ui theme used. Default is “flick” but any other theme, available under 
‘https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.13/themes/’ is usable.

Phototools: geo2wikipedia

Add wikipedia extracts to your page as a widgid, above or under your content or using shortcode's wherever you like.

Wp-Wikipedia-Excerpt vs Phototools: geo2wikipedia