OpenStreetMap
OK, I know we're not supposed to tag just for a renderer, but Mapnik is now rendering traffic lights and water towers. So now you have a reason to add those tags, if you've been holding back. Go nuts. :)
OSM has also added different viewing options for traces.
It would be nice to see a notification of changes in advance (without having to read through mail lists).
Discussion
Comment from Minh Nguyen on 18 August 2009 at 04:50
You can subscribe to this feed, which notifies you whenever the map’s stylesheet is changed. Even if you can’t read XML, you can see the specific tags and values being used by the renderer. I suppose this feed isn’t well-publicized because it would definitely lead to “tagging for the renderer”, but I use it to prioritize when mapping.
Comment from Andy Allan on 18 August 2009 at 11:42
Guys, it's fine to tag for the renderer, the problem is to not tag incorrectly just because you like the colours. See osm.wiki/Tagging_for_the_renderer