If you are looking for keywords in languages other than English, you will find Keyword Tool's features very useful. Keyword Tool allows you to pull keywords from 192 Google domains and use 83 Google language interfaces to generate keyword suggestions. That way we make sure that the generated keywords will be relevant to the country and/or language that you are creating your content for.
A service like BrightEdge comes with the biggest costs associated, but its SaaS solution for SEO covers many areas inside of a single ecosystem, including the ability to explore keyword data. This may be a benefit for agencies that wish to reduce redundancies across vendors, but eventually, it is likely that the need for a second tool will present itself as talent and effort levels increase inside of your SEO department.
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).