The following is a list of helpful user agent strings that I have found to help block bogus requests to your website. On an unknown site, you are going to see these block a few thousand attempts every day. The largest one I frequently see is Jorgee. They are vulnerability scanners which are using the default user agent. These are likely looking for low hanging fruit but nice to block them anyway. Below, I have separated my Wordfence user agent block and use the equal (=) sign as the delimiter between the string and a description. I will be updating this post when I find more and the new ones will be added at the end.
*Jorgee* = Vulnerability Scanner
*Nikto* = Vulnerability Scanner
*ZmEu* = Vulnerability Scanner