Some of the best work I've done was collaborating with Bryan Bell on themes for Manila and Radio, and icons for things like RSS and reading lists.
A river is a strict reverse-chronology of news items that conform more or less to the elements of a RSS 2.0 <item>. So you could have a title, link, description, publication date, link to comments, categories, or enclosures. There are a few other elements that can be in an item. For a full list, check out the RSS 2.0 spec. It's written so that a designer can make sense of it.
1. nytimesriver.com -- designed originally for Blackberries.
2. Arc90's rendering of the 2006-era river thanks to archive.org.
3. A screen shot of the Radio 8.0 river, in early 2002.
4. east-village.org, produced by River2.
5. Twitter is a river.
7. Les Orchard's news page (the descriptions would have to be initially expanded to make it fully a river).
8. Glowdart is very interesting. I'd like to experiment with a UI like this, but one where the user could give it any number of feeds to follow. In other words it's a nice start for a generalized RoN aggregator.