If you are looking for a particular package and don't know whether a ppa for it exists or not, then this tool can be really handy.
PPAsearch (by wrinkliez) allows you to to search a ppa right from terminal. Just type in the name of any package and hit enter. It will list you all the available ppas.
To install ppasearch type and run in terminal:
sudo add-apt-repository ppa:wrinkliez/ppasearch
sudo apt-get update && sudo apt-get install ppasearch
To search a ppa type in terminal:
ppasearch -p package name
A list of available ppas will be shown. Enter your choice to add a ppa to your sources list.
Important Note: Always check what other packages are in the ppa you chose to install. Also searching can be slow sometimes so minimize it and check it after few seconds.