craigsimps

This is a super-simple plugin which will turn WordPress’ default <code>/?s=query%20terms</code> into <code>/search/query+terms/</code> if you have pretty permalinks enabled.
This is something which I have been placing into a theme include or in a core functionality plugin until recently, but it makes sense to separate this functionality out into an individual plugin so it can be switched on and off independently.
The plugin has no administrative interface or control panel. Activation turns it on, deactivation turns it off. Once activated, performing a search using the standard WP search widget should give you a much nicer search URL.

Simple Search Rewrite

Redirects search results from /?s=query to /search/query/, and converts %20 to +.

tj2point0

Taxonomic SEO Permalinks is a simple plugin that allows you to create SEO urls based on custom taxonomies in WordPress. I personally wanted to use custom taxonomies in URLs just like built-in taxonomies like category. WordPress does support some options that helps in ‘rewrite’ of permalinks, while creating custom taxonomies. However, I found this thing is not actually working, as I tried and tested.
So I have created this plugin to fix this issue. This plugin does two major works. First, it modifies links to posts at all the places in blog and second, it helps in parsing the URLs. If you did not understand what I just said, leave it and read below.
Let me explain you with the help of an example, what we are trying to achieve with this plugin.
Consider a university website want to build a website for announcing results. The results are announced every six months (summer 2010, winter 2010, …) for various courses (BSc, BTech, …) and for various semesters (final year, second semester, …).
So we can create three custom taxonomies viz. Season, Course and Semester. What we want is SEO url with the help of custom WordPress taxonomies that will look like:
<pre><code>http://example.com/winter-2010/bsc/final-year/list-of-passed-candidates
</code></pre>
Which you can set in your regular permalink structure options just like
<pre><code>/%season%/%course%/%semester%/%postname%/
</code></pre>
NOTE: Currently this plugin do not help you to create custom taxonomies. You will need to use another plugin to create custom taxonomies.

Taxonomic SEO Permalink

This plugin helps you to set your permalinks by using custom taxonomies just like you use %category% or %postname% in your permalink structure.

Simple Search Rewrite vs Taxonomic SEO Permalink