[Zurbukz]

This new app is a great guide for new players. More experienced players might benifit from it too.

[dasDestruktion]

There are a number of great tools available (or coming very soon).

1] will be coming online soon enough after a short delayed time schedule.
2] keeps track of all of the AP amounts, information about leveling, burster levels/calculator, portal configuration, etc.
3] watches your portals and times their cooldown for the next round of hacking!
4] from the creators of Ingress (Google's Niantic Labs) is useful for finding nearby portals.
5] is a fun Ingress-style theme for your device.

For those just starting out though, nothing really beats playing the tutorials, replaying the tutorials and getting out into the game (world?) and messing around.