A Call for Communication (Half-Life) on the Steam Community (thanks Brett) now has over 6,000 members, seeking to coerce Valve into spilling some beans about their plans for the Half-Life series:

Your oldest and longest running fanbase would like some form of communication.

Waiting patiently for over four years is a daunting task, especially when E3 comes and goes without any beat of a Half-Life pulse, time and time again. Valve had stated that information was scheduled to be released towards the end of 2008, and we believe that if they have chosen, for whatever reason, to withhold this information, fans should at least be acknowledged in some way, regardless of developmental plans for the next Half-Life project. The entire trilogy of episodes was supposed to be completed and released by 2007, and if Valve have decided to do other things for the time being, that is fine; all that we ask for is a basic response on the matter, and to let fans know whether or not the Half-Life 2 story arc is scheduled to conclude at another point in time.

In addition: This message is in no way, shape or form attempting to rush the development of the Half-Life series; in fact, most members agree that Valve should take the time needed to deliver a complete and polished product.