The 70-200 f/4.0L is a great lens to start with from what you have mentioned that you want and your price range. I had a Rebel about 4 years ago and this was one of the first lenses I got. It's got great distance and the 4.0 fstop will allow you to shoot in lower light and provide that great depth of field you want in portraits. I actually know of someone who is selling his used one for $525 including shipping and paypal fees. If you are interested, email me and I'll email you his info.
The 50 1.8 is great as well. For $100 you can't beat it, but it is a fixed lens, so that takes some getting used to.
Denise Skelton
denise@skeltonphotography.com
www.skeltonphotography.com
www.skeltonphotographyblog.blogspot.com