Academic writing and web writing both use these constantly, often in the same document, which is where the trouble starts. You cite a source that lives on a site. Add "sight" — the third homophone, meaning vision — and you have three words with nothing in common but sound.
A verb. To quote or refer to a source as evidence or authority.
A noun. A place or location, physical or online. Occasionally a verb meaning to position something.
Quick way to remember
Ask whether you are quoting or pointing. Quoting takes "cite," which shares its start with "citation." A place takes "site," which shares its start with "situated." And if the sentence is about eyes, it is "sight."