I think css selectors like that would be usefull:
class="tagitem size1"
class="tagitem size2"
...
class="tagitem size6"
from 1 to 6 like html headlines, <h1> to <h6>

This is the full current renderd html output of a tag element:
<a href="http://demoshop.oxid-esales.com/professional-edition/tag/design/" class="tagitem_" style="">design</a>

A title should be applied and empty style attribute removed.
Here my proposal:
<a href="/professional-edition/tag/design/" class="tagitem size3" title="Tag: design (9 Items)">design</a>

<a href="[URI]" class="tagitem [SIZE-CLASS]" title="['TAG']: [TAGNAME]([TAG-AMOUNT] [MULTI-LANG-TEXT])" rel="section">[TAGNAME]</a>

Somthing for inspriration in tag-clouds:
http://www.smashingmagazine.com/2007/11/07/tag-clouds-gallery-examples-and-good-practices/