First I'd like to say how nice it is you're putting the effort in to help your mother get settled when she moves. And what could be more important than
finding her a good doctor. This kind of advance planning pays off down the line. I wish there were an easy way of doing this, but doctor-shopping takes leg-work. I'm a big believer in personal referrals from trusted sources. Try asking anyone you know with an elderly friend or relative for doctor recommendations. You can also ask around at senior centers and churches. People with positive doctor experiences tend to like to share the "wealth," passing along the names of their providers.
Many medical practices now have websites with profiles or background information on their medical staff. This is an excellent way to get a sense of who a doctor is beyond the name. You can do an on-line search of HMO's or hospitals in your area, then do an internal search on geriatric care or geriatric physicians. This won't rank or rate doctors, but can give you information about their specialties and even interests.
There are a number of "doctor review" websites popping up, where people rate their doctors on the site. You can find these simply by searching with "doctor review" or "doctor ratings." Most sites let you search by town or zip code. This can be helpful, but is dependent on people putting information in, so doesn't necessarily give a broad review. Great (and not so great) doctors won't be covered if no one has rated them.
In all of this it's also important to keep in mind that what makes a doctor good to one person, may not matter to another. As you look around, think about what matters most to your parent. It might be bedside manner, or gender, or a medical speciality.
Good luck and let us know if you've found any tips that can help others.