Sharepoint Crawler: "Access is denied"

Ensure the crawl account has Read access to the web application you wish to crawl. Open Central Admin -> Application Management –> Application Security section –> Policy for Web Application. Add the default crawl user here for All Zones for each web application you want to crawl. Be sure to specify the correct web application.

(Note: Find the default content access account in your SSP under Search –> Search Settings.)