How about allowing named arguments for common sizes, like IAB  (<a href="http://www.iab.net/iab_products_and_industry_services/1421/1443/1452" rel="nofollow">http://www.iab.net/iab_products_and_industry_services/1421/1...</a>) or common display sizes (<a href="http://en.wikipedia.org/wiki/File:Vector_Video_Standards2.svg" rel="nofollow">http://en.wikipedia.org/wiki/File:Vector_Video_Standards2.sv...</a>)? So you could do, <a href="http://dummyimage.com/skyscraper" rel="nofollow">http://dummyimage.com/skyscraper</a> instead of <a href="http://dummyimage.com/120x600" rel="nofollow">http://dummyimage.com/120x600</a>