Radar Jammers: These little beauties make you invisible to radar temporarily, you only get a few, so use them wisely.
Nitrous Oxide: This is one of the most popular special items in the game. It gives you a 50% increase in accleration and a 20% increase in top speed, lasting 15 seconds. You get 3 charges. A word of caution: these suckers make you go fast, and if you're not careful, you can loose control and go flying.
Blower: I use this myself, it gives you a 25% increase in acceleration, and a 10% increase in top speed, and it lasts until destroyed or removed.
X-Aust Brake: This cuts your braking distance in half.
Structo Bumbers: A must-have item, these double the strength of the front and rear chassis reinforcement, helpful if you tend to run into things a lot,(like me.)
Curb Feelers: These keep you from flipping over when you hit things sideways.
Mud Flaps: These protect your chassis from damage on rough terrain.
Heated Seats: This gives you 10% more ammunition.
Cup Holders: Make you 10% harder to hit, and guard against pistol attacks.
Dashboard Mary: This is a useful tool, it makes your weapons 10% stronger, so they do 10% more damage.
Tire Covers: They don't actually help the tires, but they give you 10% more armor.