Barry Burton - Complete Rebirth Mode as Jill.
Rebecca Chambers - Complete Rebirth Mode as Chris.
Kenneth J. Sullivan - Complete Classic Mode as Chris.

Unlock:-

Masters of Knifing  -  Beat the game once to unlock the 5 level mini game Masters of Knifing.

Wesker in wireless mode  -  Get a Rank B in Masters of Knifing.

Barry for wireless mode  -  Beat the game with Jill once

Unlockables

Special Key  -  Beat Jill Valentine's Scenario by keeping Barry Burton and Chris alive or Chris Redfield's Scenario by keeping Rebecca Chambers and Jill alive and save your game on a empty save slot. Load that save up and you will have the Special Key in your inventory. It can be useable in a room in Mansion 1F which in turn will grant you a costume change for your character. Depending on what Game Mode you play (Rebirth or Classic Mode), you will receive different clothing for each character.

Unlock Characters in Multiplayer

Barry Beat the game with Jill once in Rebirth Mode
Enrico Marini Clear all Co-op levels in Wireless Play.
Forest Speyer Complete Classic Mode as Jill.
Kenneth J. Sullivan Complete Classic Mode as Chris.
Rebecca Chambers Complete Rebirth Mode as Chris.
Richard Aiken Clear all Versus Mode levels in Wireless Play.
Wesker Get a Rank B in Masters of Knifing and beat all 5 levels

Unlock Rocket Launcher in maingame  -  Beat any scenario in under 3 hours to gain the Rocket Launcher for your next run through the game. It'll be in your inventory when you start from your completed save.