Searchmetrics - Searchmetrics Suite for enterprise companies provides SEO marketing and analytics, SEO optimization, social and content marketing.
Xenu's Link Sleuth - Xenus Link Sleuth checks Web sites for broken links.
Moz - Backed by industry-leading data and the largest community of SEOs on the planet, Moz builds tools that make inbound marketing easy.
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Dragon Metrics - Dragon Metrics is an SEO platform offering rank tracking, onsite optimization, link management, keyword research tools, & more
Integrity - Feature comparison of link checkers for Mac: Integrity, Integrity Plus and Scrutiny