Here is a list of papers from the European Institute for Advanced Management Studies.
I attended the conference in Barcelona last weekend.
Big research gaps mentioned were:
1. family unit - not enough studies in this area
2. qualtiative approaches - emerging area for family business
3. discussion about the importance of culture in family businesses - some good discussions on this.
If you cannot access the papers let me know and I will download them for you.
email me at email@example.com if you have any problems.