The YubiKey NEO

This article is much better than the Yubikey documentation - would have saved some time if I'd found it earlier when experimenting with Yubikey standard and TOTP, as that only stores a single TOTP seed per slot.

It's worth mentioning hardware TOTP tokens - the Feitian c200 is only $10 per token in small quantities, and such tokens are generally closer in concept to the Yubikey compared to a phone app (though the latter are indeed very popular these days.)