COMPLETE list of HTML tag attributes which have a URL value?

Check out the W3C's list of HTML attributes, there's a "type" column in there and just look for URI types.

And of course the HTML 5 version of that list is useful too (edit: updated link for HTML 5.2 here)

So for HTML4 we've got:

<a href=url>
<applet codebase=url>
<area href=url>
<base href=url>
<blockquote cite=url>
<body background=url>
<del cite=url>
<form action=url>
<frame longdesc=url> and <frame src=url>
<head profile=url>
<iframe longdesc=url> and <iframe src=url>
<img longdesc=url> and <img src=url> and <img usemap=url>
<input src=url> and <input usemap=url>
<ins cite=url>
<link href=url>
<object classid=url> and <object codebase=url> and <object data=url> and <object usemap=url>
<q cite=url>
<script src=url>

HTML 5 adds a few (and HTML5 seems to not use some of the ones above as well):

These aren't necessarily simple URLs:

SVGs can also contain links to resources: <svg><image href="url" /></svg>

In addition, the style attribute can contain css declarations with one or several urls. For example: <div style="background: url(image.png)">

So you can include:

<style>
    #domID {
        background:url()
    }
</style>

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