Can anyone tell me the difference between a "28-80 f3.5-5.6 III Ultrasonic" and a "28-80 3.5-5.6 IV Ultrasonic"?? Are the "III" and "IV" just revs of the same lens or is one better than the other??

Also, if you were a beginner and buying your first Canon SLR camera, what single lens would you get if you could only have one?? A 50mm fixed? A 28-80 zoom? Other?? I'll be shooting mostly the family, kids, travel, etc...nothing professional or fancy.

the III and IV are versions of the lens, yes.
I can't find them on the Canon website though.
It does list these ...
EF 28-80mm f/3.5-5.6 II
EF 28-90mm f/4-5.6 II USM
EF 28-90mm f/4-5.6 III



How about the 24-70 2.8 L ? It's the lens that is on my camera most of the time.
Will the extra stops be worthwhile to you?
How about the fast ultrasonic motor, with full time manual focus?
If I had to have only one lens, it would be this one of my 4.

Also consider the 28-135 IS
It does have a wide zoom range, so that may impact image quality.
But I really appreciate the IS in difficult lighting as I can hand hold successfully at lower shutter speeds. That's why I have the 70-200 2.8 L IS