DLC I like adds interesting characters, works as an expansion pack (new abilities/areas/story and so on), and stuff that's integral to the game in general (movesets and maps in Dynasty Warriors for example). So good DLC for me is stuff like Dragon Age 2's Mark of the Assassin, and bad DLC is crap like "Overpowered Weapon Pack 2" for the same game.
I can't really say what my favorite example of DLC is, because if I like the game, I probably like most of the DLC already (although I'm really excited for Brave New World coming out for Civ 5). The worst example of it is obviously horse armor from Oblivion. To think of something less (or more, depending on your perspective) slimy, SFxTekken's bullshittery with disc-locked content that you bought a key to unlock.
I can't really say what my favorite example of DLC is, because if I like the game, I probably like most of the DLC already (although I'm really excited for Brave New World coming out for Civ 5). The worst example of it is obviously horse armor from Oblivion. To think of something less (or more, depending on your perspective) slimy, SFxTekken's bullshittery with disc-locked content that you bought a key to unlock.