What is live view on digital cameras?
All but the most basic DSLRs now offer the option to compose your images using the rear LCD screen instead of the optical viewfinder. This is known as live view. This can be especially useful when shooting from ground-level, or from tight angles.
One thing to bear in mind is that when using live view on your DSLR, the autofocus system will generally be slower than when using the optical viewfinder.
What to look out for when buying a camera with live view
As long as you aren't trying to capture fast-moving action this shouldn't be too much of a problem.
It's also worth noting that Sony and Olympus have come up with a solution that works around this, and now offer faster-focusing live view AF.