@impulsivity

used game sales actually help new game sales (not directly)

Let's say all I do is pirate games. No money is transferred and devs don't earn anything. No new copy was ever bought. No other people have extra $ in hand to buy new games. Nothing is stimulated.

Let's say all I do is buy used games. Money is transferred from me through the trading facility (ebay/amazon/gamestop) where they pay for their copy. The person who handed in the used copy in the first place probably bought it new (at some time a new copy was bought). Now with extra cash in hand, he goes out and buys another new copy to keep himself entertained.

Now, gamestop may rip you off when it comes to buying used (buy back for $20, sell for $55), but Amazon/ebay only take ~10% of the price, and the prices are typically significantly lower than new. So, while I may not be willing to spend more than $20 on a game, someone else may want that $20, add it to his $40 and buy a brand new game.

The only thing destroying the used game market will do is slow down the people who buy loads of games and then trade them only to buy more new games. It will also stop people like me (who don't generally buy used anyways) from buying a game. I can't say it will encourage more people to buy games.

Don't forget Downloadable Content.

Joe buys Rad Racer 6 used for $5. He finds the game to be awesome! Joe notices for $5 more he can get all the new cars to play with off of XBL. Joe just gave the developer some of cash, despite buying the game used.

  Most people who sell games use things like that gamestop card that adds 10% to used game values when you sell.  That card, not coincidentally, lets you also take 10% off used games.  This encourages people to sell 2 used games for say 50 bucks (25 each) and then buy a discounted different used game for 10% off (or around the same 50 bucks).

   In effect they are doing constant 2 for 1 trades in Gamestops favor and GS is taking endless 50% "fees" for the transactions.

   I asked the guys in GS about this when I was buying FFXIII when I saw the guy in front of me trade in games and they sold him on that 10% card.  They said most people trade used for used since its "the best deal" and you can usually find new releases used just a few days after release (when the power gamers beat them).

Again, all those "powergamers" are buying new, and selling used. You just proved my point.

I don't deny there are people who buy used games, but they fund the people who buy new games.

  I agree with the DLC point.  I like the Battleforge model actually (its a really fun RTS game that uses the trading card game model).

  The game is free with limited cards and then you can buy more content (in this case more cards for more elaborate decks) for points which are only available from the publisher.  The devs have said that a lot of people who start free end up spending more then the retail price of a lot of titles.

  Another good example is dungeons and dragons online, since going free to play (with microtransactions) it has actually made more money then it ever did with a normal box price and sub model.

   If more games went free to play initially with microtransactions I think it would be beneficial to all involved.  I'd be happy to pay a token amount (say 10-20 bucks) to get the initial disk with some content and then add on to it if I like the game.  It also removes A) the draw of the secondary market (since most of the content is purchased outside retail channels) and B) the risk of paying 60 bucks for something that might suck since you pay a lot of the DLC money after you're already sure you like the main game.

  I think Burnout and Borderlands have done a nice job with making useful DLC and working paying for extra content into the mix as far as consoles go, but theres a long way to progress on the console side I think.  Most of the free or cheap initial game plus microtransaction DLC momentum is on the PC side of things.

True, but I think the publishers will gain more customers overall.  I think more used game buyers will decide to pay the extra $5 for new and become a new customer to the publisher, than new game buyers will decide not to buy at all.  And anyone who buys new with the idea of selling it used soon after, would be better off and save more money by renting or going with gamefly.

while you may gain some new customers, you may block other customers from entering the market cheaply and growing into buying new. You essentially make the market less accessible by forcing everyone to buy $60 games. And true, renting makes more sense, but people are stupid. Now, I don't know which would be more beneficial to gaming overall, but I do know that the used market isn't as bad as pirating.

I also know that Nintendo never complains about the used market and their games hold their value better than pretty much anyone else (check out videogameprice charts for some actual analysis), but they do find piracy to be a big problem. They also turn a healthy profit without having to worry about the used market.

Out of the "techniques" listed, I think going with the "bonus" content for a new purchase is the best method. They slightly hurt the used market without resorting to totally destroying the value of the game you bought or resorting to extreme DRM.