Learn about 10 tools that can help you see your website the way Google's algorithm does so you can improve your SEO.
1) Google Webmaster Tools
Cost: Free
Also See : Things You Should be Doing in Google Analytics
2) Check My Links
Cost: Free
3) Moz Pro Tools
Cost: Free 30-day trial, then paid plans from $99/mo - $599/mo
4) SEO Report Card
Cost: Free
5) HubSpot's Website Grader
Cost: Free
6) Woorank
Cost: Free 14-day trial, then $49/mo for a Pro Plan or $149/mo for a Premium Plan
7) Screaming Frog SEO Spider
Cost: The Screaming Frog SEO Spider LITE version is free (with limitations*), and the paid plan is $160/year
8) Found's SEO Audit Tool
Cost: Free
9) Remove'em
Cost: $249 per domain or a subscription option starting at $99/mo
10) Varvy's SEO Overview Tool
Cost: Free
Source: http://blog.hubspot.com/blog/tabid/6307/bid/33164/6-SEO-Tools-to-Analyze-Your-Site-Like-Google-Does.aspx