There are free services and paid services, but if you want to check out the competitors site here are a couple suggestions: 1. semrush.com - free and paid service 2. keywordelite.com - paid service These are the two main ones i use for SEO spying. I also use tools to check out competition on the keyword level. I use: 1. Micronichefinder - paid 2. Market Samurai - paid
I totally agree with Dipali. Yahoo explorer is on of the best tool to analyze competitor's websites. I always use it.