I guess most of us know Duckduckgo, but I just wanted to highlight the !Bangs option. I have some search engines installed on my browser, but !Bangs are really useful shortcuts. I.e. typing on duck:
!dimensions "public libraries"
gets you the results for that query on Dimensions.
the same for that but on Pubmed.
There a lot of Academic Bangs, even for specific university libraries, etc. And for more other categories.