Here are some unlockables by category. These are not Resident Evil 5 PC Cheats, but it is helpful knowing what each play-through unlocks in the game, and what each unlockable does. Just so you can decide to play a particular way to unlock the one you want.
Filters – Achieved by completing the game on “Amateur" difficulty. These alter the look of your game; “Classic horror" filter looks black & white, “Retro" adds sepia tone and “Noise" adds a slightly fuzzy-effect to the game, so it looks like a bad VHS camera.
Outfits – Dress up your character with some unique outfits. To unlock all outfits in the game, achieve “A Rank" in these areas: Experimental Facility, Ship Deck, The Village, Ancient Ruins, Public Assembly, Missile Area, The Mines and The Prison.
Uber Weapons – You need to fully-upgrade the following weapons (if you want use “unlimited money" from the trainer or item-duping): M92F Pistol, S&W M29, Ithaca M93, VZ61 Machine Gun, S75 Rifle.
These upgrades unlock (in order with the above): Beretta 83R, S&W 500 Magnum , Hydra Triple Barrel Shotgun , Gatling Gun (Chris), Longbow (Sheva).
For more tips and a comprehensive list of achievements, visit this Resident Evil 5 PC Cheats page.