The word squid is usually used as singular or plural, examples: Singular: A squid was caught on my line. Plural: The restaurant had a tank of live squid on display. That being said, some people do squids as the plural form.
If you mean the ocean animal, then the plural is squid. Although squids is probably acceptable and only an absolute pedant (like me) will tell you it's wrong. If you mean a superconducting quantum interference device (SQUID) then the plural is SQUIDS.