Run & Gun (extra weapons, extra combat rules)
Gun Heaven 3 (guns!)
Bullets and Bandages (advanced medical rules)
Another Rainy Night (Fiction with some rules, can be converted to 5th ed)
Sail Away Sweet Sister (Fiction, 5th ed rules)
Vladivostok Gauntlet (Fiction, 5th ed rules)
Stolen Souls (update on the metaplot, Location book (Manhattan), primer on doing B&E jobs)
Splintered States (an intro adventure book)
Coyotes (rules for crossing border)
The Assassin's Primer (discussion on being an assassin)
Many sourcebooks are faily edition agnostic and can be used with 5th ed.
6th World Alamanac
Most Location books (Montreal 2074, Corporate Enclaves, Runner Havens, Seattle 2072, Land of Promise, etc)
Spy Games
Conspiracy Theories
... the list goes on, really.