Funcom offers a memberships fee system for its conspiracies MMO.
"With this recent change there is no reason not to join and take part in The Secret World," claims Joel Bylos, Game Director of Funcom's conspiracies MMO; he and the developer are hoping going free to play will tempt more gamers into the grand conspiracy. Pay Once, Play Forever, claims the latest trailer but, if you really want to, there is a Membership option to speed things along.
The subscription element of the game has been completely removed. You buy it - which will run you about $30 - and get access to all the content, plus the Initiate DLC pack should you buy before December 31st. If that's where you want to stop, no problem; but Funcom's hoping you'll be tempted by the Membership option, which offers faster experience gain, item-of-the-month gifts, and game store discounts to those willing to fork out a monthly fee.
Future developments in The Secret World will come courtesy of DLC packs, the first of which - the Initiate pack - is due in January 2013, and will cost $5 if you didn't take advantage of the December 31st offer. The DLC packs aren't the same thing as patches, which will include free content and updates to the core game. Those will still carry on as normal; the DLC packs are intended as icing on the cake.
There's a FAQ over here if you want to learn more.