Utkarsh Kukreti

This plugin enables embedding of multiple stylesheets and javascript files on a per-post basis.
Multiple file names should be separated by a ‘,’. Extra whitespace after and before a ‘,’ are automatically ignored.
Relative paths to files are automatically prefixed by the /css or /js. These settings can be customized by editing values of the variables $css_folder and $js_folder in the plugin file.
Absolute paths are directly hotlinked.

Include Custom Files

Enables embedding of multiple stylesheets and javascript files on a per-post basis.

mneil

Finds all possible .js and .css files from a WP install available and allows you to combine and/or compress the files to reduce 
load time. The plugin can monitor file changes in “development” mode (by hashing file mtime) which allows the plugin to 
recompile the files when a file changes. Or, it can cache the files in “production” mode so that files are only recompiled 
if they are not found or are deleted manually from the cache folder. Additionally, this plugin will allow you to force the 
inclusion of javascript files into either the head or the foot of the page.
There are two modes, development and production, the ability to force the files to print in the header or footer*, the use of 
Google Closure as a JS compiler, and finally the ability to pick and choose which files, including dependencies, should be combined.
*forcing head compiles can fail on JS files queued after the call to wp_head(). The plugin will, in this case, render the late 
queued files in the footer as originally intended.

MnCombine

Easily manage the merging and compression of js and css files from plugins and themes

Include Custom Files vs MnCombine