These are my resources for etymology, generally in order of usefulness.
The Oxford English Dictionary is widely recognized as the world's best historical dictionary, offering attestations of words as they developed through history. Extremely useful, but it costs a fee unless you can get it through an academic institution.
This is undisputedly the online Bible of etymology. Plug in almost any English word and almost any proper noun, and etymonline will come through for you. One of my main sources for posts and a very reliable etymology site.
Another great online resource, providing etymology clues etymonline missed or wrote differently. A wonderful website that shows not only etymology, but also pronunciation, definition, and usage of words. Really good if you need etymology of foreign words.
r/etymology (which I moderate), r/linguistics, and r/etymologymaps are fantastic sources of inspiration brimming with hundreds of thousands of like-minded language enthusiasts! I highly recommend checking out those subreddits.
This is perfect. If you want to see the prevalence of a word or phrase over time in literature, this site is amazing. It can tell you how any given term increased or decreased, from 1900 to 2000. The internet is so useful sometimes!
Any serious etymological research has been published somewhere, and Google Scholar is the perfect tool to find it. Honestly, I have no idea how people got along without it before the Internet.
A collaborative website covering all kinds of linguistics topics, but great when you have an etymology question that needs to be answered, for etymologists lurk at every corner, waiting to strike.
A blog run by Oxford Dictionaries, this site is updated everyday with some new post about the English language. Naturally, this sometimes coincides with etymology, and their information is well-researched and reliable.
not as comprehensive in their etymological explanations as etymonline or wiktionary, dictionary.com is nevertheless a wonderful tool for the purveyor of word origins. It also shows a really neat map pinpointing the location of origin, a unique feature.
Etymologies provided in this site are no better than Merriam Webster's, but it's more for the Anglophiles out there. Besides, if you really want to make sure your word is accurate, you should use as many sources as possible.
If you're looking for the etymology of hard-to-find words, dictionary.com has a much better user experience, though about the same amount of information is offered.
This site, the most visited one on this list, is useful for etymological lookups in some instances, and normally provides a similar experience as Wiktionary (a wikipedia site) does. However, Wiktionary is probably better for linguistics, though the latter is good too.
The Inky Fool, a blog administered by Mark Forsyth (the author of the Etymologicon), a professional etymologist and linguist, is not great as a reference source but fantastic if you're just randomly searching for etymological trivia.
This site tells you how frequent a word search is on google, and is exceptionally useful for etymologizing modern words: you can see how interest has declined or increased over time. Great for neologisms.
This site helps clear up a lot of my linguistics questions and occasionally delves into the world of etymology. Really useful for a student of grammar, moderately useful to a student of word origins.
This question-and-answer site has several linguistics questions responded to, and is mildly helpful for select searches. Basically, this is the English Stack Exchange, but less nerdy and less helpful in most cases.
Yet another discussion forum online for etymology. While it is much less reputable than the English Stack Exchange or Reddit, I've found myself using it occasionally to find links to other references or get ideas.
If, under "Language" you go to "etymology", you can find an etymology blog by etymology professor Anatoly Lieberman, whose posts are less frequent but more detailed than mine; an excellent resource.
Dartmouth College somehow got hold of this awesome student who posts etymology of every body part on his website. Basically anything related to human biology has its etymology identified on this site, though it's not really that good for any other types of etymology.
Primarily a myth-debunking website, there are some etymological myths debunked on this site, and that has been very helpful in my crusade to learn word origins. Not a reference or leisure site for etymology in general, but still valuable and accessible.
I rarely use this site, but they do have a linguistics zone which is occasionally helpful, though most of the answers are essentially the same as those offered on sites with less cringy formats.
This nerdy website is good for any kind of trivia, and they occasionally throw out some very cool etymologies you would not expect. Good, but the Inky Fool is better for that kind of thing.
So these sites technically have little to do with linguistics, but they've each published a few etymology cartoons and are FANTASTIC nerdy havens for inspiration.