The Laser Sight is an attachment that raises accuracy by around 1-5% for Assault Rifles, Submachine Guns and Pistols. The downside to having this attached is that anyone can see the laser dot, so it might give your position away. When under water or in smoke, the beam itself can be seen, drawing a straight, bright red line right to your position.
The Silencer is an attachment that suppresses the sound of the gun, making it harder for the enemy to hear your shots. It also reduces spread a little. All weapons except the SR8 , SPAS , HK69, and Desert Eagle can use this attachment.