The Bing Keyword Research Tool is available free of charge but you do have to jump through a few hoops first,before you can use it!
It’s well worth it though because here is a free keyword research tool that does a decent job and offers a viable and useful alternative to that other well known free tool, Google Keyword Planner.

The Bing Keyword Research Tool sign in screen.
The main difference between the two is that the Bing Keyword Research Tool doesn’t supply its suggested keywords from paid search data, as Google does, but from organic search results taken from their own search engine. This means that the results you are given would normally be different from those you would get from the Google tool but would not include any indication as to their cost if you were to use them in a ppc campaign.
It is worth noting that, if you have a Bing Ads account then they do have their own version of Keyword Planner that does include a bid price estimate.
The Bing Keyword Research Tool has a “Strict” option which is equivalent to Google’s own Exact Match parameter and which focuses the results on just the keywords entered and nothing else whereas the default, which is without the strict option chosen, will return the equivalent of Google’s “phrase match” setting which will return results that include the selected word(s) in the context of a larger phrase.
For example, if you use the keyword “email marketing” and do not select the “strict” option Bing tells us that there were 1137 searches made for that search term in the last six months whereas if we do select the strict option and do the exact same search the number of results drops to 577.
N.B Results shown are taken from UK based results, in English only.
There is a facility to export the data and you can save your favourite searches so that you don’t have to keep re-entering the data if you want to update your keyword research. Bing also shows the trend data for each word or phrase which enables you to see any seasonal trnds in search traffic and which broadly equivalent to the data given by Google Trends although the Google tool goes back as far as 2004 if you really want to deep dive whereas the Bing data.
You can find the Bing Keyword Research Tool here, but you will have to set up a Microsoft account, (free) before you can sign in and use it.