Olympus OMD E-M5 lenses
Suzie... as others have pointed out you can use virtually ANY lens ever made on a M4/3 camera if you have the proper adapter for it. But you will not have autofocus, since in order to have that you need lenses with electronic parts that are specially designed for that particular camera. And this is true for every camera made, not just M4/3 cameras.
However, there is no shortage of lenses available for M4/3. There are currently around 30 auto focus lenses available from Olympus, Panasonic and Sigma. And there are an additional dozen or so manual focus lenses made by other makers that come with M4/3 lens mounts, so they will not need adapters.
Suzie... I don't know what you budget is, but you can get substantially the same image quality from a much smaller and cheaper Olympus EPM2 or EPL5 if you are willing to give up weather sealing, an eye level finder, and a pro grade build quality. Both those cameras use exactly the same lenses as the OM-D does.