SpyFu is a competitive intelligence tool for search marketers. You can type in a domain to see all of the keywords it ranks for (including the content that ranks), the ads it buys on Google, and an estimation of how they compare to their competitors in the marketplace. You can also type in a keyword to find the domains that buy it, the domains that rank for it, and how that has changed over time. With deep insights into both SEO and PPC, SpyFu is a solid tool for people who are starting a campaign and those who are improving what is already in motion.