In Eve Isk, capacitor is life. It's not surprising that the most commonly used rigs are energy grid ones. The single most used rig is the Capacitor Control Circuit, the Tech I variant of which provides a solid 15% boost to your ship's capacitor recharge rate for a measly 100 calibration and no drawbacks. That makes them as effective as a Tech I capacitor recharger, so it's not uncommon for people to slap three of these tasty treats onto their ships.

Fitting some Capacitor Control Circuits will often free up valuable mid slots normally used for capacitor generation. Mid slots being arguably the most useful slot, used for shield modules, electronic warfare, sensor boosters, microwarpdrives and afterburners, it's not surprising that people would endeavour to free them up using rigs.

Another popular rig is the Ancillary Current Router, a rig whose Tech I variant boosts your ship's powergrid output by a pleasing 10% for the same 100 calibration as the capacitor rig, again with no drawbacks. This is equivalent to a Tech I reactor control unit and could free up low slots you might need for armour tanking or modules to help you deal more damage.

Additionally, capacitor rigs are extremely useful in shield tanks. It's now possible to use an X-Large shield booster and have it run permanently, making the Raven an even better mission-running tank than before. Other useful options include the shield rigs for recharge rate and hitpoint amount. Those rigs, combined with the new Tech II shield power relays, have turned passive shield tanks from second-class tugboats into something incredibly scary. This year may very well be a good one for the Caldari pilots out there.

LESS USEFUL RIGS
Some rigs, unfortunately, fall under the category of fairly useless, possibly a waste of a rig slot and your ISK. One example is the Warp Core Optimizer, which decreases the amount of capacitor required to warp a given distance. While this sounds like something that might help new pilots with low skills, it requires just as many components to build as many other rigs, rendering it as expensive as more useful rigs like the Capacitor Control Circuit.

The Emissions Scope Sharpener and Memetic Algorithm Bank rigs increase the chance to be able to open archaeology and hacking containers respectively with their given module, Analyzer for archaeology and Codebreaker for hacking. Given that the only places to find these cans are in COSMOS complexes or explored profession sites (see p58), both of which require a decent combat ship, most players will simply fit either an Analyser or Codebreaker to their combat ship. Since access difficulty simply determines the chance of the can opening on each of an unlimited number of attempts, these two rigs are completely replaceable by a little patience - something that doesn't cost 200 calibration and a rig slot. Also, contrary to the more popular superstitions out there, using these rigs will not improve the loot found in the cans.