Whats a good lense for a Rebel XT

[setiprime]

King- Consider a few things first. Assuming your son is young and not walking yet - he's inside most of the time. Fine for now. Is he going to be playing outdoors this fall?
A BIG mistake many people make is buying gear that is 'adequate' for what they think will satisfy their immediate needs.
Aside from your son expanding his horizons - what happens if you grow in your photography?
A comparetively 'cheap' kit lens will quickly end up in the back of your closet and has no resale value other than a reminder of your mistake.
The XT is not a camera to underestimate as to capabilities. Put a decent quality, decent range, reasonably fast lens on it and then have REAL enjoyment.
What us old timers know is that the lens is as (if not more) important than the box you mount it to.
If you want to mess around with a "general" decent lens - buy the Canon 50mm f1.4 - they are a good all around beginning lens. $75.00 or so. surprisingly sharp !

[EOSThree]

The 50 f/1.4 is around $300, while the 50 f/1.8 is around $75. The 1.4 does have a metal mount and is a half stop faster than the 1.8. Either lens would be a great lens to start with, although a little limited indoors by their equivelent focal length of 80mm(just a little long).
setprime is totally correct though when he says the lens is as imortant or more so than the "box"(body) it is attached to, I would say more imortant in every way though. A great lens on a Dreb will blow away a poor lens on a 1D. Garbage in = garbage out, and a photo taken with a poor lens no matter what body will result in a comparitively poor photo.

[Arctirus]

I can't say enough good things about my EF-S 17-85 IS USM.

[trexuphigh]

28-135 is a good al around lens. Get it with a hood and a UV filter and you'll use it alot.