Search lobbying firms and the clients (e.g. companies, non-profits, local governments) they represent at the state and national levels. Also has an "explore lobbyists by specialty" section that lets you identify a subject of interest from an alphabetical list and find lobbying firms for that subject area.
"Combine[s] data on campaign contributions, legislators’ votes on bills, and information on the interests supporting and opposing those bills in the United States Congress and the California State Legislature. Our federal lobbying data set adds further dimension to this picture."