Here are the ones I actually use.
w https://www.google.com/search?&q=site%3Awikipedia.org+%s&btn... first result from wikipedia
h https://www.google.ca/search?q=site%3Anews.ycombinator.com+%...
r https://www.google.ca/search?q=site%3Areddit.com+%s reddit
y https://www.youtube.com/results?search_query=%s youtube
m https://www.google.ca/maps/search/%s google maps
b https://builtwith.com/?q=%s add "b " to a url to find out what tech is being used
wo https://www.wolframalpha.com/input/?i=%s wolfram alpha
i https://www.google.com/search?tbm=isch&q=%s google image search
g https://github.com/%s "g upspin/upspin" to jump to https://github.com/upspin/upspin.git
br https://github.com/Homebrew/homebrew-core/blob/master/Formul... read homebrew formula