I'm sitting here with my eight year old daughter who is in the middle. She has a sister who is 12 and a younger brother who is 5. She wants to hang out with her older sister and her friends, but is excluded most of the time. And, she is to old to play the things her brother wants to play. She has other things to do, but always wants to play with her big sister. :( And, there are not many kids her age in the neighborhood. How do we solve this middle child syndrome as they call it??

I don't know that you can solve this issue. She IS the middle child. You can help her find her own interests - be it sports or dancing, etc. she will find friends.
But you can't change her birth order.

Check with the local recreation department, larger churches with youth activities, and the YMCA. Become a soccer or softball Mom. Also, Brownie Scouts and Blue Birds.

Whatever you do... do not force the older child to take her little sister everywhere. That will just make the middle child feel like a burden, and the older child will resent her.

I agree with the others--get her involved in some interest, especially something like dance or martial arts or tumbling--something she needs both her body AND her mind for. Music is another good option. Something that she learns WITH other kids, but can do on her own as well.

Does she have school friends that don't live close that you can set up play dates with her parents? Does she have something she really wants to do (besides play with her sister!) that you can encourage here?