What lens?

Hi all. I have a Canon 300d with the 28-55mm lens. I have been looking for a lens with a longer focal length for a while, never really serious unless i came upon a REALLY good deal. I think i am ready to buy now. I have looked at the Canon 75-300mm III USM and the 75-300 IS. I would love to have the IS, but it is out of my budget right now, but i have read some reviews that are not too flattering of the USM. Anyone own the 75-300 III USM and are you happy with it? Is there another one i need to look at (a different Canon, Sigma, Tamron, etc.)? Or should i wait and save up for the better lens?

Just so you will know what i will be doing with this lens: 1. My son (9 years old) plays soccer, i would like to get him in action. 2. I go to a few NASCAR events (some day, some night) during the year, and l like to take a few photos there. 3. We make a couple of trips to the Smoky Mountains each year and i like to get soem shots of some of the plants and wildlife. 4. I will be traveling for work to 2 places that i have never been before in the next 4 months and want to be able to "reach out" to get some good photos if necessary.