Password generator
Strong, truly random passwords generated on your own device using system-level cryptography. No password is ever sent or stored anywhere.
The randomness here is the real kind
A randomly generated password is only worth as much as the randomness that made it. Here the characters are drawn with the browser's cryptographic generator, the one browsers provide for keys, not with the «random number» function used in games: the difference is that the latter is predictable if you know when it started, and for a password that's a fatal flaw. And the password doesn't leave your browser: it isn't sent to anyone, and this page keeps none of them.
Length matters more than symbols
This is the point nearly everyone gets backwards. Adding a symbol to an eight-character password makes it a little harder; adding four characters makes it thousands of times harder, because every extra character multiplies the combinations by the whole alphabet. With letters, digits and symbols, each added character is worth nearly six bits: going from twelve to sixteen characters multiplies the tries needed by over a million.
The practical rule: at least sixteen characters where the service allows it, and no fewer than twelve. The «one capital, one number and one symbol» rules many sites impose don't come from this arithmetic: they come from the idea of preventing «password», and they push people into writing «Password1!», which is exactly the first thing an attacker tries.
A different password for every service, and somewhere to keep them
The way passwords get stolen is almost never by guessing: it's that some website suffers a breach, and from there the same address-and-password pair gets tried on every other one. That's why the only defence that works is for every service to have its own, and since nobody remembers them all, you need a password manager: the browser has one, and there are programs that do nothing else.
Where the password has to be remembered by heart (the computer's, the manager's own) a phrase of words works better than a string of symbols: four or five words picked at random are memorable and longer than any password you could hold in your head. For that there is Passphrase generator.
Nearby tools
For a numeric code there is PIN generator, for a phrase of words Passphrase generator and for technical identifiers UUID generator. If you have to send protected files, rather than a password on the message, the page is Create a ZIP with a password.