One I just recently discovered is symbolhound.com. It's nice because it lets you search for characters that google absolutely refuses to treat as search terms. I needed to debug some makefiles and bash scripts the other day (not my strong suit!) and it helped me understand some of the weird syntax I was seeing.
As others have mentioned, Google no longer respecting literal search terms has made it much worse for many types of searches. DDG had been great at this, but sadly has been following in Google's footsteps the past few years.