The book I'll work on after this is an "Agent's Guide", which is basically the player's guide with a description of the Department of Law hierarchy, a few option character variants within that hierarchy (such as SWAT, Internal Affairs, Undercover Agents, PSI-Squad, etc.), maybe a lifepath system to flesh out a character as they are being built, and a few ideas for how games by be run outside the regular shift structure to reflect an Agent's life when they aren't on patrol.
Beyond this, I'm thinking of a series of Splatbooks to flesh out the setting, or more accurately provide tools that a group can use to flesh out the setting as appropriate to their game.
For example, the "Management Guide" would provide a variant lifepath system for Management characters, a system to quickly generate management oriented NPCs, a few pre-generated NPCs to drop straight into a scene or investigation, a guide to creating corporations (altruistic or sinister), and a few notable corporations that might exist in the setting already.
Something similar would be done as a "Street Guide" but using gangs instead of corporations, a "Cult Guide" would use zany religious groups, etc.
In addition to these, I'm tninking of a "Quartermaster's Inventory" book that follows the cyberpunk game tradition of a book filled with equipment. It'll probably be presented in the form of a catalogue, or Department evidence log.
(Equipment Guide Inspiration)
At the speed I develop projects, this range of books should keep me going for a decade or so... I'll probably get bored and move on to something else before it's all done.