If you are looking for Keyword hunting, then you will probably need Wordtracker for your SEO or PPC expedition. Wordtracker is an online keywords gathering and analyzing service which base is data on 
Google user entry. This mean that each keyword result you will find is given by the keyword entered by users and the number of time this specific keyword has been searched for. By getting the right keyword and the most searched, you get your site more authoritative, getting an higher impact in search result and human needs, have a more qualified website traffic, getting you more conversions and increase your revenue.
Then imagine if instead of getting only one keyword people are searching for, you get thousand of those! Seems pretty interesting? Wordtracker can also give you undiscovered keyword allowing you to be the first to exploit the niche, import your keywords list, customize your research, save your project for later and allow you to check the keywords competition on multiple search engine.
You can take their 7 days free trial if you want to test their service or if you already set your mind, you can order for monthly or annual subscription which worth the investment that pays for itself quickly. If you have change your mind, they offer a within 30 days money-back guarantee.
I personally use Wordtracker and have ordered their full years membership and strongly suggest to buy one of their membership. If you can’t afford to buy the full-years subscription then you should consider to try at least their monthly subscription. Especially if you are doing SEO, Wordtracker is an asset you can’t pass over as you want the same for your ROI (Return Of Investment)!