Congo, it really depends on what your budget is to be honest and the worst conditions you think you will be shooting in.

Ones off the top of my head:

Canon 70-200 f4L if you are going to be shooting mainly in daylight or good light situations. This will run you around $550 to $600 depending on where you get it.

Sigma 70-200 F2.8 This is a great budget lense that a few on here get great results out of and runs depending on where you get it for $750-$850 depending on where you get it. Use this in moderate to low light situations.

Canon 70-200 F2.8L This is the lense that canon users want. Great color reproduction and awesome glass. I would recommend this over the Sigma if you can afford it. This one will run about $1150 or so. Use this same as the sigma.

If these are still too much for you then you can pick up a 70-300 USM F3.5-5.6 for around $150. It is not ideal for low light but it will give you the extra zoom you are looking for. I started out with this lense and still use it to shoot races.

Another option that I have never used but it could work is the Canon 28-135 IS (Image Stabilization) F3.5-5.6. Great zoom range and would be about what you would be shooting on track or just walking around. This lense runs around $350-$400 but is not that great of a low light lense.

There are tons more out there but this was just off the top of my head not knowing what budget you have.