During the beta phase of Planetside 2, EMP grenades would lock vehicles for a certain amount of time and also lock infantry weapons. This is no longer the case and they now instead, drain the shields of infantry(friendlies included) and also remove the HUD and the overlay for HS/NV scopes. They can also be used to drain cloaked infiltrators to decloak them, and currently will deshield a Heavy Assault if they are using their shield ability.
More grenades equal more information. "Information is Ammunition."
Or Nanoweave because you can survive one more extra shot.
Cloaking Devices (special ability, default key is "F"):
Hunter: Default cloaking device, most snipers will take this.
Nano-Armor: This cloak will allow you to take more damage when used but at the cost of using your energy supply faster than the Hunter Cloak. Nano-armor also regenerates twice as slowly as the Hunter Cloak.
Stalker: A newer version of the cloak, it does not degenerate if you are standing or crouching still. The perfect cloak for Spotters since their role requires them to sit and keep enemies spotted. However, using this takes away your primary weapon, so any cloaking device will suffice for the Spotter role.