If you love Sleeping Dogs (and you really should), you won't be running out of content anytime soon: next month and possibly beyond a slew of DLC will launch, some free and some paid. Among the contents: boosts, costumes, and money (some of which can already be unlocked by playing), and also new missions and weapons.
First up is the Street Racer Pack which adds more street racing and possibly boat racing, then there's 20 cop missions in the SWAT Pack, and a crazy strong weapon and armor set in the Tactical Soldier Pack. Those are all paid; the free stuff comes in the form of the Community Gift Pack, though there's no details as of yet on what's in it. Finally, there will be a story-driven expansion -- full details on that at New York Comic Con on October 14.