Both Portal and HL2 Episode 2 have been updated earlier and the release notes pointed out something weird - "Changed radio transmission frequency to comply with federal and state spectrum management regulations" - which doesn't make a lot of sense taking into account the fact that it's a video game we're talking about here.
Any way, it’s a series of secret messages, which are activated by carrying an in-game radio to several in-game locations and the some of them sound pretty close to GlaDOS which is awesome.
members of the Steam forum have ascertained that some of the sound files contain hidden images, visible when run through a Slow Scan Television (SSTV) application, images such as equations, skulls, keyboard buttons and the Aperture Science logo (woot!).
Now, the link to the thread on the Steam forums that documents this is here for those interested and so far it hasn't been the whiny stupid talk that usually goes around there.
I really love how Valve keeps the community engaged via the blogs, the dev commentary, contests and real-life stuff such as the postcards and comics from TF2 and this move they just made is purely awesome in my book.

okay...
does that mean more HLverse games are being made? and Valve is slowly starting a promotion?

I hope so.

Ep3 coming soon? (as in this decade!) Yay!

Probably. But this decade has just begun, so expect Ep3 around 2019.

2 Minutes to Midnight on new years eve.

If you crack the code, then the space-time continuum rips open and the G-man will personally visit you.

It's been fun to read what they've discovered. EP3? Sure hope so, I've pretty much lost interest due to the wait, but I'll likely still get the thing sometime. More interested in more Portal though.

Portal was one of my all-time favorites... but i'm not too sure if i want more. I worry it'll fall into Tony Hawk territory where they're essentially just retreading the same old ground, but with a few pointless extras added in to justify (and dilute) the experience.
If they can do it justice though...

Unless Valve has some completely different surprise planned it has to be either Portal 2 or Episode 3, so either way people will be happy.
Well, that is until they convert its release date into Valve Time.

Hm. Nice.

That's one issue I have. If they keep it polished and short with not much in the way of 'new' features, I'd still be happy if it's just another 2-3 hours long.
There's a lot of community maps, but I've found most are badly done, or are designed for people with insane twitch skills. Part of the reason I enjoyed it was that you could take the game slowly and carefully.

I vote for Portal 2, anyway....

I vote for Portal2=Episode3

Episode 3 = Portal 2 = Left 4 dead 3 = Counterstrike something.