Amarr = White Noise
Caldari = Spatial Destabilizer
Gallente = Ion Field Blahdeblah
Minmatar = Phased Inversion ECM

Electronics - Improves CPU for all ships, allowing more/better modules to fit.

Engineering - Improves powergrid for all ships, allowing more/better modules to fit.

Signature Analysis - Improves targeting speed.

Weapon Upgrades - Lowers CPU requirements for gun or missile modules. See also Advanced Weapon Upgrades.

Navigation - Increases base speed for all ships. Better chance of catching up to, or escaping from enemies.

Evasive Maneuvering - Increases ship agility, reducing align times and allowing closer orbits at higher speeds.

Energy Systems Operation - Increases capacitor recharge rate, which is necessary for almost all modules.

Energy Management - Increases maximum capacitor capacity.