Health Power-up
One of the most useful and sought after power ups. These are easily identifiable as they glow red and show up on the radar when you have suffered enough damage.

Weapon Power-ups
All the weapon power-ups look the same, and which you get after picking one up is more luck than anything else. As well as being notified about which powerup you have received, your reticle will change giving you a better aim and approximating the trajectory.
There are three different types of weapon power-up: Speedy, Bounce-back and Area Effect.

Speedy
With a fast reload time and much quicker projectile speed, these light missiles will streak through and will inflict the same amount of damage as a regular shell from a medium tank.
Bounce-back
Bouncing projectiles which will inflict splash damage affecting any tank close enough to where it explodes.
Area Effect
A large shell that takes longer to reload but will do more damage and has a large area of effect.
Reload Gate
Driving through this arch will replenish your ammunition supply. These gates are marked on your radar as small pale blue circles. When you are low on ammo, they will flash on your radar.

Bounce Pads
Driving over these will vertically boost your tank propelling you upwards in the direction you were travelling.

Booster Pads
Driving over these arrow pads will give you a sudden boost of velovity in the direction of the arrow. These can be very useful to get around the map in a hurry. On some pads, the arrow will change direction each time it is used (so that any pursuer will not be able to follow you so quickly!)

The Scrum Ball
In scrum games, one of these will spawn at a random location on the map and will slowly bounce around until a tank picks it up. Once it has been taken to the goal, a new one will spawn. The scrum is carried on top of a tank and can be stolen by a well coordinated shunt or by destroying the tank carrying it.
The scrum is shown on the radar (if you are within range) as a white dot.

The Goal
In scrum games, one of these will spawn at a random location on the map and will remain in place until either the scrum bounces off the edge of the field of play or someone carries the scrum inside it and scores.
The goal appears on the radar as a purple circle and this will flash if you are carrying the scrum.

Text and images taken from http://www.planetthinktanks.com/about-objects.asp