I am currently creating a firefox addon which you should be able to easily donate bitcoins to site owners that provides bitcoin address.
What about a new robots.txt directive for bitcoin donations? It could be something as simple as:
User-agent: *
Disallow: /files/
Disallow: /admin/
Sitemap: http://example.com/sitemap.xml
Donations: 171RLtavSkiKoDGSboatMNJ9dqpvjYSesR
Perhaps the word 'Donations' here is inappropriate, as Bitcoin has many uses, but it could be a simple way for webmasters to broadcast their Bitcoin addresses in a universal, simple way.