Common words:
* Spirit
* Spire
* Spiral
* Aspire
* Inspire
* Expire
* Conspire
Less common words:
* Spiracle (an opening, especially one in an insect's body)
* Spirochete (a type of bacterium)
* Spirant (a consonant sound made by expelling air from the mouth)
* Aspirate (to inhale or breathe in)
* Dispirited (lacking in spirit or enthusiasm)
* Transpire (to occur; to become known)
Words with "spir" as part of a larger root:
* Respirator
* Respiration
* Inspiration
* Expiration
* Conspiration
This list is not exhaustive, but it gives you a good starting point. You can find even more words by searching online dictionaries or using a thesaurus.