Help me choose 1 Lens

Hi everyone, I have been reading all the posts and am now really confused as to what lens to buy. (I have 1 20d and the 18-55efs and 100mm sigma macro). I would like to pic your minds for some advice...

I want to shoot nice indoor photos of my new baby,as well as use this new lens for general purpose. Later I will add a longer zoom for outdoor stuff,sports,etc.

Now I am considering:
Canon 50mm 1.8 (because it will work fast indoors/no flash)
Tamron 28-75 f2.8 (everyone here likes it alot)
Sigma 24-70 2.8ex dg macro(is it as good or better than tamron?)
Canon 28-135 IS (the Is will improve my low-light,slower speed pics?)

My guess is that the 1.8 or 2.8 would give me the best indoor shots. I like having a zoom, but if the 1.8 is of great value for my purpose, let me know.
So, my budget is limited and I just want to buy one lens for now, but another one soon- would the 50mm and 28-135 be the best all around combo for most types of photos and which lens of all of them(or another) will give me the best baby shots?

Thank you for your comments, I look forward to hearing them, and posting some great pics...

For what you'll be doing, the 50/1.8 is the best budget choice. The only other lenses that I would suggest you consider are the 50/1.4 or 85/1.8. The 50/1.4 would help just a little with the low light, and possibly give a slightly sharper image; the 85/1.8 would help you get closer. The downside of these lenses is higher cost, of course. In addition, with the 85/1.8 would need a little more shutter speed to freeze camera shake since it's longer, and consequently, you might have to crank up the ISO and get a little more noise.

I wouldn't recommend any of the zooms for that application since it sounds like you will need extra aperture to deal with low light. Also, the larger aperture will help you get less depth of field and separate the subject from the background. Indoors that's a big issue since so many distracting elements will be close by the subject.

Whatever you do, set a custom white balance using a grey card. Nailing the color down will get you much better looking shots in most instances.

I might go for the 50 and a off cam flash. That would be a nice combo for baby pics. Hell the flash would make F/stop unimportant with about any lens mentioned too.

The IS won't help taking photos of people in low light, especially if the people are moving. Taking pictures of hills in low light with that would be fine.

Personally i'd get the Tamron. I've stopped using my 50mm F1.8 because I got a lot of out of focus shots, whereas with the 50mm F1.4 that I replaced it with they were fine. I think the focus motor's inaccurate, according to the Canon tech who calibrated the 1.8 (which gave no improvement).

An external flash would be great investment if you can afford it.