Here's an older study(pdf) that at the effects of different types of training in men.  Subjects were split into three groups - endurance training only, strength training only, and concurrent strength and endurance.  In a nutshell, the results were:

• The endurance only group lost fat mass but also lost lean mass
• The strength only group gained lean mass but had no change in fat mass
• The concurrent group lost fat mass AND gained muscle

What was unique about this study was that it also measured changes in metabolic rate.  The groups had the following changes in basal metabolic rate after the training period:

• The endurance only group had a decrease of 48 calories per day
• The resistance only group had an increase of 113 calories per day
• The concurrent group had an increase of 82 calories per day

So while the resistance only group increased basal metabolism the most, this group did not perform any cardio, and hence their total energy expenditure wasn't high enough to cause fat loss.

The clear winner is obviously the concurrent group.  There was some of the interference effect, with the concurrent group not gaining as much strength as the resistance only group and not gaining as much aerobic capacity as the endurance only group.  But to me, this is just splitting hairs.  For the average person who is trying to get into shape, performing strength and endurance work provides the best of both worlds - muscle gain and fat loss.