Update: OK, so at least one person wanted it as a plugin, so feel free to download Intermittent Date Headers.
Here’s a code snippet that’s not really worth making into a plugin. It’s designed to put date headers into your main post listing page. As an example, you could end up with:
Heading: March, 2008
Post: dated 15th March
Post: dated 28th March
Post: dated 29th March
Heading: April, 2008
Post: dated 1st April
Post: dated 4th April
Continue reading Interspersing your post listing with date headers in WordPress