What is a good Canon Digital Camera that has interchangeable lenses that takes great family and scenery photos?

Any of the Digital Rebel SLRs will meet your needs. The least expensive model currently is the Rebel XS.

The 50D is a nice upgrade - more features and more durable construction, but may be overkill for a casual photographer.

If you're going to spend additional money, I would buy better lenses before buying a more expensive body. I suggest the EF-S 17-55 f/2.8 IS (about $950) - this is an outstanding general purpose lens, MUCH better than the cheapo kit lens that comes with the low end Rebels. The 24-105 F4/L is another outstanding choice.