Dmytro Shteflyuk

Permalink option of WordPress <code>%category%</code> has one great limitation – 
when this option is selected, WordPress uses category with lowest ID for 
permalink generation. This plugin is intented to bypass WordPress permalinks 
limitation and allows you to select category for permalink generation.
<h4>Support</h4>
If you have any suggestions, found a bug, or just wanted to say “thank 
you”,– feel free to email me <a href="mailto:kpumuk@kpumuk.info" rel="nofollow ugc">kpumuk@kpumuk.info</a>. 
Promise, I will answer every email I received.
If you want to contribute your code, see the Development section under 
the Other Notes tab.
<h3>Development</h3>
Sources of this plugin are available both in SVN and Git:
<ul>
<li><a href="http://svn.wp-plugins.org/scategory-permalink/" rel="nofollow ugc">WordPress SVN repository</a></li>
<li><a href="http://github.com/kpumuk/scategory-permalink/" rel="nofollow ugc">GitHub</a></li>
</ul>
Feel free to check them out, make your changes and send me patches. 
Promise, I will apply every patch (of course, if they add a value to the 
product). Email for patches, suggestions, or bug reports: 
<a href="mailto:kpumuk@kpumuk.info" rel="nofollow ugc">kpumuk@kpumuk.info</a>.

sCategory Permalink

Plugin allows to select category which will be used to generate permalink on post edit page. Use custom permalink option %scategory%.

Rick Radko

This plugin removes the ‘/blog’ slug from the main site permalinks of a sub-folder multisite install. The intended purpose for this plugin 
is for multilingual installations where the main site is the default language (although I’m sure there are other applications). These sites 
are of often for businesses where having the ‘/blog’ in the permalink (URL) does not make sense.
‘/blog’ is automatically removed from the main site permalinks upon plugin activation.
‘/blog’ is automatically restored in permalinks upon plugin deactivation.

R3DF Multisite Blog Slug Remover

Removes the '/blog' slug from the main site permalinks in a multisite.

sCategory Permalink vs R3DF Multisite Blog Slug Remover