Ripgrep is my essential codebase search tool. It's incredibly fast, very clear, and it just works how I expect. I use it a lot if I'm refactoring a larger codebase, particularly because it works well for more dynamic languages (where a compiler won't help) and for comments and documentation (where I want the naming to remain consistent).

I've heard good things about Bat and Exa - I personally have never felt a huge need for them, but other people claim that they're pretty essential to them.