1) SEMrush - I believe that among all the 3rd party software, SEMrush has the largest keyword database. Their search volume data is pretty accurate and aligns with the Google keyword planner. Also, based on the type of content that needs to be produced (i.e. informational, transactional, etc.), one can utilize different filtering options available in it.

I’ve found google trends to be an interesting way to see if a keyword (and by extension a niche) is growing or shrinking, and whether it’s seasonal or not. I can’t think of any other tool out there that can reliably tell you this information, so that’s really useful. Also, if you’re building a site, especially an authority site, getting onto something that’s trending upwards is a fantastic idea.

This is a really straight-forward strategy. Contrary to popular opinion – small niche websites can actually still work. Basically, you create a small website that is hyper-focused on one long tail keyword. You create the very best resource on that specific topic and publish the very best content on the internet based around that long tail keyword. Monetize with something simple like Adsense, Amazon or another affiliate product – then just sit back and watch the money roll in every month!
You can try DeepMiner. It is good for scrapping, rank position, generating long tails and keyword suggestions. You can export the data to document for later analytics. You can find popular keywords that people are searching for. 7 major engines are supported, Google, Yahoo, AOL, Amazon, YouTube, Ask, Bing. It supports multi-threading so it is very very fast scrapper. BTW you must use proxy list if you plan to scrap thousands and thousands of keywords.
In a nutshell, Long Tail Pro helps you quickly find keywords in bulk based on a seed keyword that you input.  In addition to returning hundreds of related keywords, the tool also shows search volume (monthly search volume), advertiser bid, number of words, rank value, and my favorite Keyword Competitiveness (helps you judge the competition and keyword difficulty).