I know most that I've seen posting here about online flight are using VATSIM, however, for those that might have been using GameSpy to access multi-player flight and are looking for an alternative now that there's no more GameSpy access for FSX there is a web site that's been created that lists a variety of alternates including VATSIM and several other services.

Here's the link: http://www.fsxbeyondgamespy.com

We could always set the online server back up here as well if there is an interest....