A long discussion on the subject is here (currently on the front page of MilesBuzz).

One tool favored by Flyertalkers is the program developed by FTer KVS.

Flyaow.com also has a list of tools.

In the meantime, since the question isn't really directly related to miles and points redemption, and there are plenty of other current threads on the subject, I'm going to close it here.

If you have a specific question, feel free to post on a current thread or traverse the Mileage Run and TravelBuzz forums.

Regards,
Gary
aka gleff
MilesBuzz and Delta moderator