Most custom search engine has a random option. All previous search strings are stored in a text file and I can recall search text from many years back. Very interesting to see results that one has forgotten. Also with this you don’t have to search for keyword from Google keyword planner, Google search engine was best search engine there you will get all information which your require and also provide lots of option which help you to select has per your requirement.
Below are best sources to find information that you don’t know exist
1. Trending searches
2. Real time topic trending
Finally for me there is no particular software or tool. Manual research marketing works for me.