Em Shreve

This plugin implements gzip output compression to speed up load times.
The plugin also does a check to see if browsers are incorrectly saying that they do not support GZIP when they actually do. This can speed up load times for a significant portion of users.
<pre><code>For requests with missing or mangled Accept-Encoding headers, inspect the User-Agent to identify browsers that should understand gzip.
* Test their ability to decompress gzip.
* If successful, send them gzipped content!
</code></pre>
See:
<ul>
<li>http://www.stevesouders.com/blog/2010/07/12/velocity-forcing-gzip-compression/</li>
<li>http://en.oreilly.com/velocity2010/public/schedule/detail/14334</li>
<li>http://wpdevel.wordpress.com/2010/07/13/forcing-gzip-httpwww-stevesouders-co/</li>
</ul>

Force gzip

Implements gzip output compression to speed up load times and does a check to see if browsers are incorrectly saying that they do not support GZIP whe …

sdesalas

This plugin allows your WordPress blog to output pages compressed in gzip 
format if a browser supports compression.
HTTP compression generally means a 60-80% REDUCTION in the size of your pages 
(broadband usage) as well as an INCREASE in download speeds of 3x to 4x.
To test if your blog is using compression use the following link:
http://ismyblogworking.com/
Check “Page GZip” on the right hand size. 
Check “Bandwidth saved by compression” on the left hand side.
NOTE: This plugin should not be used alongside WP Super Cache or WP Cache 
since those plugins are already implementing compression. Your blog 
will keep working but those plugins will stop caching new pages.
RECENT NEWS – 20 March 2010:
Its been reported by a user that there is a conflict 
using WP HTTP Compression together with Google Analytics Plugin (3.2.5). I’ll 
to look into this and release a patch for next release. 
Note that this conflict is NOT with Google Analytics itself but with 
the PLUGIN. Google Analytics scripts and stat collection have been tested 
and work fine with the WP HTTP Compression plugin.

WP HTTP Compression

This plugin allows your WordPress blog to output pages compressed in gzip format if a browser supports compression. HTTP compression generally means …

Force gzip vs WP HTTP Compression