Stylus Reviews
The original authoritative review by Serenity Caldwell at Macworld. Serenity also provides a followup resource at Macworld with a complete buying guide.
The Verge gives the same overview in case someone doesn't read Macworld.
I'm sure Serenity will get her hands on the Adonit pressure sensitive stylus soon to provide a full review.
I use the Cosmonaut stylus but the Adonit looks superior for drawing fine details.