The Google AdWords API announced the new beta version of the AdWords API, i.e. API v2009, is available for all advertisers to give a try.
Note, there are significant changes and improvements made to this API. The rate sheet for API calls shows a reduced rate and new features are coming, such as asynchronous calls, partial failure acceptance, keyword optimization tools, and reporting.
If you are using the current API (v13), it is important to start looking at this new API, especially this one, since it is significantly different from the current API. Version 13 will likely be retired in early 2010, so prepare as soon as you can.