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EDIT NOTE

As Brian kindly pointed out, Ding King is a DIY tool rather than a franchise operation. I was thinking about Dent King when I replied below. I have no experience with the Ding King tool.

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There are a number of paintless dent removal (PDR) companies out there, Dent King apparently being one of the larger ones. I believe these are sometimes called spooners. These are typically franchise operations with mobile units that service dealerships and quality used car lots. I did a bit of research and used a local company recently with very good results, although they couldn't get out all the parking dents I wanted dealt with.

These can be very cost effective solutions to dent problems provided:
o the paint is undamaged (no flaking) -small chips can be touched up later
o the dent is not so wide or so deep as to have significantly stretched the metal
o the dent is not at a body panel crease or corner where the paint would crack as the dent is worked out
o the technician performing the dent removal is well trained and experienced -this is the most critical aspect as paintless dent removal is very much an art
o you are willing to put up with some minor scuffing or scratching on the back side of the dent where it is worked out -unless they use the expensive plastic tipped dent removal tools

A good dent removal will be virtually invisible, even viewed from a shallow angle under bright light. Amazingly, access to the back of the dents is rarely an issue, although sound deadening material may have to be chiselled away. They have the tools to get to almost any dent, often without removing interior panels.

Charges are basically on a time basis, but rates for such skills are not cheap.

Apart from simple comparison of cost to a body shop fix, which often results in a body panel replacement, the biggest advantage of PDR is that you get to keep the original finish paint and clear coat. Even the best blended-out paint jobs can be noticeable under the right conditions, especially as the car ages. This can really pay off down the road if you're trying to sell your car in first class condition and as accident free.