You might find something at http://www.ciplets.com/ though it's more developer-oriented I believe. There are a few apps at http://www.ccmstuff.org/.
In addition, while it doesn't provide phone services itself, the Cisco IP Telephony Users Group (CIPTUG) has hosted contests in the past for phone service bake-offs:
http://www.ciptug.org/
Many companies create phone services and market them individually rather than collectively as well. If you are looking for something in particular, someone here might be able to help you in either the end users or this (the developers) forum. The app might already exist or someone could create it for you.
Hope that helps!
