For the past 20 years video and computer games have risen as the greatest selling form of media in the United States. But for many companies, that is simply not enough.

A new trend designed within the past six years or so has finally taken root in the gamer culture. Downloadable content to update your game in a number of different ways, from new firearms in Battlefield: Bad Company, to entire new worlds in Everquest 2.

Most often, these can be classified into one of two categories: free or paid.

Free content is usually minor. They come in the form of bug fixes or modules most frequently. However, in the case of Massively Multiplayer games, large game updates are frequently free and add quite a bit. In the case of World of Warcraft, the newest patch has added an entire island, dozens of new daily quests, a new five-man instance and a new 25-man instance, setting the bar far higher than any previous content in the game.

Paid content, however, is often far different. As mentioned before, these are usually whole new weapons, levels or even planets. Mass Effect recently received a large content boost with Bring Down the Sky. It contains a whole new storyline taking place in the Asgard system, introducing an entire new race of aliens. It sells for 240 points on Xbox Live, and is should add about 90 minutes to the game.

Expansion packs are large packages of content containing whole new worlds, brand new features and hundreds of new items. The only problem with expansion packs is that they often cost $20 or more. But the sheer amount of content available pales in comparison to other purchasable items.

Of all the content I've purchased, I have to say the only product that has really left me satisfied is offered by BioWare. The creators of Baldur's Gate, Icewind Dale, Jade Empire, Mass Effect and a dozen other titles, are incredibly adept at creating quality games and keeping them fun for years after.

In particular, the game Neverwinter Nights had incredible replayability. BioWare designed both free and purchasable content at regular intervals. Entire new adventures popped up from time to time, including the sweeping epic of Kingmaker where the player travels throughout an entire country to gather support and eventually become the monarch of a rising empire. Or the Infinite Dungeons pack, providing a massive hack-n-slash style dungeon crawl with seven crafty boss monsters that are amazingly well thought-out.

However, for every good experience, there is a poor one. The Elder Scrolls: Oblivion offered a bizarre add-on on release, giving the user the option to purchase armor for their horse. It was literally useless.

For two dollars, you could make your horse look shiny, but it offered absolutely no use otherwise. Believe me, I was not happy after that purchase.