1. Any fics where Tony and Bucky meet and they end up becoming friends/best friends/buddies. Extra points if Steve is surprised or jealous of their friendship. Extra extra if Tony works on Bucky's arm a lot.
2. Pretty much the one above but with a Tony/Bucky relationship.
3. Or one where Bucky and Tony actually knew each other before Steve found him somehow and everyone is just confused.
4. Specific fic- Bucky is incredibly fond of Tony and lights up whenever he's in the room, calling him russian nicknames. And everyone knows but Tony is confused i think by Buckys behavior towards him. It was on ao3.