I am going to use some terminology here too (to standardize it):

• Virtual Currency - Fixed

Games from companies like GPotato, Acclaim, Nexon, Game Campus, etc. use this model. You pay "n" real world for "m" virtual currency, which may be separate from game currency (most likely is). The virtual currency is often shared between multiple games. This does not require keeping a cash pool.

• Virtual Currency - Dynamic

Games like There and Second Life use this model. The value of money changes dynamically with supply and demand, a fixed amount of money is added into the economy slowly over time. Currency might be withdrawn at any time, to create cash. This requires keeping a cash pool.

• Subscription

This is the model used by Sony, many NC Soft titles, etc. where you pay a monthly subscription for access to the game. Often is combined with lifetime subscriptions and with discount subscriptions. Some companies (SOE for example) offer some discount model for multiple titles.

• Boxed Game

A game on some form of media (probably CD/DVD) in a box, sitting on a store shelf

• Game Time Cards

Cards for Subscription titles available in retail stores

• Game Currency Cards

Cards for the Virtual Currency Models

• Downloadable

A game that is available via d direct download from the public Internet

• Pay Per Play

A game that charges per play session (or for groups of play sessions). Meridian 59 used that model at one point, you paid per week you played, if you did not log in for a week, you also were not billed.