HL2: Episode 3 is not the surprise
The E3 surprise unveiling set for Valve's Portal 2 slot is not Half-Life 2: Episode 3 says Valve.
Gabe Newell has gone on record saying that the recent teaser is a fake and the surprise is definitely not the long awaited third episode.
All the speculation is apparently a load of rubbish so apparently the guessing game is back on again.
Although this may have ruled out Episode 3 if hasn't ruled out other possibilities like Half-Life 3 or perhaps something even juicier. All will be revealed at E3.