GroupRinger allows you to assign tones(ring or text and custom) to a group of your contacts.
You can also easily manage your groups and members. Create, delete and rename groups, assign members to them.
Fully supports iOS5 new features, like custom texttones and having one of your texttones as a ringtone or vice-versa.
This app won’t see Exchange groups nor contacts(GoogleSync included), only the ones synced with iTunes or iCloud
There is also a lite version available here.