In my capacity as an editor at InfoQ I recently had the opportunity and privilege to edit the November eMag on API Technologies. If you haven't had a look at it yet, then feel free to download and take it with you.
The great thing about this task was that I got to read and review a lot of interesting content on APIs. The down-side was that only a small fraction of that could fit into the eMag. In the end we selected seven articles that I think captured a broad and comprehensive range of topics across APIs from the business end, through API design, architecture, tools and security.
As an aside or a footnote, I wanted to publish here a list of other articles, news items and conference presentations that I enjoyed while researching the eMag. I've broadly categorised them into the following subject areas.
The Business of APIs
API Design
Architecture & Scalability
Case-Studies
Tools & Integration
This list is by no means exhaustive and there is new material being added all the time, but I think if you browsed through even half of this material you'd have a good overview of the state of the API art.