If your cat appears to be stuck in a tree, then you should visit this site:
The website includes information on what to do and when to contact a professional. There is also a Directory of professional tree climbers who rescue cats.
If you cannot find someone locally on their directory, then check with your local animal control, shelters, landscapers, and gardening supply companies for a possible referral to a professional arborist.
There are a few companies that are willing to travel or have multiple locations across the US.
There is also an interesting article on Arboreal Cat Rescuer Techniques, but they strongly recommend that you contact a professional rather than attempting to climb up and get your cat yourself.