For years I've maintained two particularly handy utility modules: StringUtils (various methods for working with strings) and ArrayUtils (same, but for arrays). For a long time, they were hosted at the site of my now-defunct email replacement company, Verex.com.
But VerEx closed its doors years ago now, and while I hate breaking links, it's time to move these to a more permanent home on my personal website. So you can now find StringUtils and ArrayUtils here: http://strout.net/info/coding/rb/
Note that while many of the other code samples on that page are by now a bit outdated, StringUtils and ArrayUtils are still up-to-date, and I end up using one or both of them in almost every project.
If you happen to have any bookmarks or links to either of these, please update them.