75-300 IS USM or 100-300 USM

[r_m_aten]

As a new 10D user, I want to buy a telephoto lens mainly for some nature photography and sports (I'm not a pro, just an enthousiast). So here's the dilemma:
I can get a 100-300 USM fairly cheap (330 euro). I can get the 75-300 IS USM for 570 euro. Is the image stabilizer worth the extra 240 euro? Is the lens still usable at 300mm without IS?
I'd like to hear you opinions.

[bwb s30]

get the 70-200 F/4 L Lens ... best glass available at a reasonable price .. you'll never regret the purchase

[RichardtheSane]

I do have to agree about the 70-200 F4, a very good lens indeed and very reasonably priced.
However if that is still out of your price bracket then I recommend the 100-300 USM. I have this lens and it is a joy to use and suprisingly sharp for the money. I have seen samples from both the the 100-300 and the 75-300IS and I can see the difference in sharpness as the 75-300 can be soft wide open.

At the end of the day, do you need to use slower shutter speeds at the 300mm end?