Brainage,
The first camera I bought I felt it was necessary to get a lens with a long range zoom. I shelled out the cash for a generic 70-300 and spent the next 4 years continuously cursing my decision. The AF was slow, the sharpness was poor etc etc. This may have improved, particularly with the IS lens, but I doubt it.
In your position I would take the time to research a good "standard" lens or the highest quality you can justify, and get good with that. Use that time to save some money and get a good high quality zoom 70-200 L (one of the 4 available, depending on what you decide you need).
If seems you have committed to this by stepping up and buying the 50D, I just think it would be a shame to reduce the quality of your images by using lower end glass.
You will get a range of different opinions on this, and there are lots of previous threads about the pros and cons of just about any combination imaginable.
Good Luck!
Kf