I am still missing an easy block for e.g. placement in the header which allows a quick & easy registration via ajax.

One example is the "ViperBar" -> http://www.viperchill.com/viperbar/

It should contain an "optional" name field and an e-mail-adress field.
Also maybe a "hidden"-value for the newsletter if there are multiple ones available.

Feedback (Thanks or error-message) should be displayed via ajax in the same block.