It has become common practice to use CDNs for caching javascript, css, font’s and more…
however this does not appear to extend to icons to the same extent (possibly because each site prefers to have a unique look and feel?)
Are there widely used icon sets hosted by CDNs that are common enough to provide significant speed improvement from the CDN hosting and possibly already being pre-cached from another site using that CDN.
One example is:
http://cdnjs.cloudflare.com whose contents are browse-able at https://github.com/cdnjs/cdnjs/tree/master
some icon sets it hosts are at:
/ajax/libs/twitter-bootstrap/2.3.2/img/glyphicons-halflings.png
/ajax/libs/fatcow-icons/...
/ajax/libs/foundicons/3.0.0/svgs/...
/ajax/libs/aui/5.4.0/aui/css/icons/...
/ajax/libs/topcoat-icons/0.2.0/svg/...
/ajax/libs/jqueryui/1.10.3/css/base/images/...
*jqueryui is also hosted on ajax.googleapis.com and others but is a limited set
as is the bootstrap halflings icon set:
http://netdna.bootstrapcdn.com/bootswatch/2.3.2/img/glyphicons-halflings.png
http://ajax.aspnetcdn.com/ajax/bootstrap/2.3.2/img/glyphicons-halflings.png
http://www.bootstrapcdn.com/twitter-bootstrap/2.3.1/img/glyphicons-halflings.png
How about hosting them yourself on Amazon CloudFront? It should only cost pennies a month depending on your traffic.
Though first of all, make sure you’ve optimised the icons you’re using by turning them into a single sprite file. That may resolve the need to use a CDN at all.