Currently Online 
I think providing the incentives to buy new (like the bonus content in Batman Arkham City and Mass Effect) or to hold on to games for longer (like the Season Passes in games like Gears of War 3 and Forza 4) are the way to go. It doesn't stop people from buying second hand but rewards first time buyers. Homefront also worked in the way it implmented the online pass. Online multiplayer was still fully accessable to everyone but if you didnt have a pass your level was capped, which still allowed for the full experience and wasn't much of a competitive handicap.
Standard passes to simply access the online servers, such as for Dead Space 2 (where the multiplayer only existed so EA could put an online pass in the game) and FIFA where they offer no extra content are counter-productive.
Banning used game sales completely will just promote piracy, as would Microsoft's rumoured plan of stopping used games from being played.
