There is an excellent book by Susan Golombok called, 'Parenting: what really counts?' It's a review of all the scientific evidence on what children need for healthy development, and it looks at divorce, single parenting, same sex parenting etc. It's a fairly dry book, but short and really accessible.
Inevitably, there's a lot of 'it depends'. Take my own situation: I was raised by a single parent and it's very obvious to me that we paid a price. I was one of three children, my mum worked FT, we were latchkey children, and there simply wasn't enough parental resource to go around. In many ways my mum was amazing, but I did have a pretty lonely and stressed childhood. You would think that having siblings would have helped, but actually we were locked in rivalry for her scarce attention.
It was not ideal. However, it was better than life would have been had my dad stayed (almost psychotically violent, chaotic alcoholic).
I am now a lesbian parent. My children have plenty of male role models (not least an involved father, albeit not in the home). My understanding is that the weight of the evidence is that children are not psychologically disadvantaged by having same sex parents.
I reckon it's much more about resources than about structures. Children need plenty of time, attention, love, stimulation from parents who are not stressed, distracted, depressed or at war with each other. It's harder to give that if you have just one parent (but there are many, many brilliant single parents). It's also harder to give that if there are two parents in conflict with each other. It's harder to give that if you are unemployed, if you have no extended family support, if you have mental health problems, if you live in a war zone...