Of course, for the most part I rely on people who create projects to promote them on their blogs, Twitter or elsewhere. Nonetheless, the following resources are especially valuable.
Web Developer Focused Sites
CoDrops has some of the most attractive and impressive demos and tutorials around. However, for the purposes of our discussion, Manoela Ilic (Mary Lou) also produces a weekly list of the best projects, tutorials and other posts around HTML, CSS and web design.
Web Developer Focused Newsletters
I've covered this topic before more generally, but these newsletters always lead me to good projects.
Both of these newsletters maintained by Peter Cooper (the latter with the help of Axel Rauschmayer) always contain a list of new and updated projects. Somehow, this list always manages to include projects that were completely off my radar, but deserving of attention.
Web Tools Weekly
This newcomer on the newsletter scene is by Louis Lazaris and it is entirely focused on new and updated libraries. The first issue came out this week and hopefully this becomes another valuable resource.
Yes, it is tough to wade through the noise on this site, but frequently a gem will shine through. Keep in mind that this isn't always on the front page, but often is passing mostly ignored on the very busy newest feed.