There are quite a few things you can unlock in the multiplayer side of Dead Space 2 for PS3, Xbox 360, and PC. Here is the full list of items you can unlock, and what level is required to unlock them.
Level 4 – Solid Army Green Suit
Level 7 – Line Gun
Level 8 – Solid Red Suit
Level 11 – Force Gun
Level 13 – Solid Black Suit
Level 14 – Increased Magazine Size for Plasma Cutter
Level 16 – Solid Olive Suit
Level 17 – Seeker Rifle
Level 20 – Urban Camo Blue Suit
Level 23 – Urban Camo Army Green Suit
Level 25 – Increased Magazine Size for Line Gun
Level 26 – Urban Camo Red Suit
Level 28 – Javelin Gun
Level 29 – Increased Magazine Size for Force Gun
Level 32 – Urban Camo Military Suit
Level 33 – Increased Magazine Size for Seeker Rifle
Level 34 – Increased Weapon Damage for Plasma Cutter
Level 36 – Urban Camo Olive Suit
Level 41 – Tiger Camo Blue Suit
Level 42 – Increased Weapon Damage for Line Gun
Level 44 – Increased Magazine Size for Javelin Gun
Level 45 – Tiger Camo Army Green Suit
Level 46 – Increased Weapon Damage for Force Gun
Level 49 – Tiger Camo Red Suit
Level 50 – Increased Damage for Seeker Rifle
Level 52 – Tiger Camo Military Suit
Level 56 – War Torn Suit
Level 57 – Increased Weapon Damage for Javelin Gun
Level 59 – Visceral Games Suit