Whats the difference between these two lenses? Canon EF 75-300mm f/4-5.6 III USM Telephoto Zoom Lens for Canon SLR Cameras and the Canon EF 75-300mm f/4-5.6 III Telephoto Zoom Lens for Canon SLR Cameras. All that I see the that the USM is missing from the second one. What is USM? And is it better to have a lens that has USM?

Is there a comperable price lens that has better quality than the Canon EF 75-300mm f/4-5.6 III USM Telephoto Zoom Lens for Canon SLR Cameras?

USM = Ultrasonic Motor.

The USM equipped units are faster to focus, quieter, and more reliable over a longer period of time(for most users).

Have you looked at this Canon link:
http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&fcategoryid=150&modelid=7444#ModelDetailAct

about the USM version of the lens?

Also you can manually overide the focus with a USM equipped lens.

I just want to point out that these are about the least expensive lenses Canon offers and a bit of a dog if you ask me.

OTOH they sure are cheap.

I have not tried these two lens but did try one 3rd party of the 70-300mm range and you had to keep it on a tri-pod or a mono-pod to even get decent photos from it.
Couldn't afford the L-Glass 100-400 but chose the Canon 70-300 IS. I feel this is a good lens for the price.

http://rovowen.smugmug.com/photos/284797048_QZ3JA-S.jpg