Photo: Etan J. Tal, CC BY-SA 3.0, via Wikimedia Commons
One example. Colors, sub-models, and production years vary; the machine you find may differ.
Introduced by IBM in 1961, the Selectric replaced the typebar with a spinning, tilting golf-ball element. The carriage stays still while the element moves, so it is quieter, faster, and more reliable than any portable that came before it. The Selectric II added correction tape. For long sessions and dense pages, it's still the fastest manual-feel machine you can buy used.
External, in their original form. The people who know these machines best — click through to read and watch.
Listings come and go. These show whatever IBM Selectric I / II machines are on the marketplace right now.
See IBM Selectric I / II listings on eBay marketplace
Some links here are affiliate links. If you find a machine through one I get a small share at no cost to you, and it doesn't change which machines I point to.