Mark Jaquith

This simple plugin (no configuration) redirects <code>?s=FOO</code> search URLs to the nicer <code>/search/FOO</code> versions. Requires pretty permalinks.

Nice Search

Redirects search URLs from ?s=FOO  to /search/foo and converts spaces to + symbols

haukep

This plugin disables WordPress’ URL autocorrection guessing feature. 
If you for example enter the URL <code>http://www.myblog.com/proj</code> you won’t be redirected 
to <code>http://www.myblog.com/project-2013</code> anymore.
This plugin is based on the example here: https://core.trac.wordpress.org/ticket/16557

Disable URL Autocorrect Guessing

It's not really needed because the code can just be put in functions.php, but this does make it easier for people who don't know anything about PHP.

Works Perfectly

Disables WordPress' URL autocorrection guessing feature.

Nice Search vs Disable URL Autocorrect Guessing