Some cognates that don't look like cognates:
come, v.
venir, v. (French)
From Proto-Indo-European *gwem-, *gwm-. In the Germanic branch, /g/ > /k/, giving *kweman or *kuman. The English word comes from the second stem, which in Old English appeared as cuman. The letter o comes from scribal use before m or n to avoid misreading.
In Old Latin, the PIE sound /gw/ simplified to /w/. In Vulgate Latin, this became the /v/ sound that remains today. I'm not sure what caused the /m/ to change to /n/, but this isn't a big issue; nasals frequently change place of articulation.
quick, a., n., and adv.
vivant, p. ppl. (French)
bios, n. (Greek)
The same sound changes applied here. The PIE word was *gwiwo-, which became vivus in Latin and *kwiwoz in Proto-Germanic. The origin of the second /k/ is unclear; Gothic didn't have it, but all the Northern and Western Germanic languages do. I'd guess it was influenced by the first /kw/. (The English sense was originally "living," as in "the quick and the dead.")
In Greek, the /gw/ sound became /b/. This sounds really bizarre, but it's fairly common. The /g/ is a voiced velar stop (back of the tongue against the soft palate), and the /w/ is a labiovelar glide (lips rounded and back of tongue raised). We oten get ready to start making the next sound before we've stopped making the current one. Speakers stop using the back of their tongue to make the stop and start using the lips instead. Then the /b/ and /w/ simply merge and leave only the /b/.