Valve have revealed who will be doing the voice cast's in the Half Life 2 game...

Robert "Benson" Guillaume will play Dr. Eli Vance, a benevolent scientist and fellow survivor of the first Half-Life's infamous Black Mesa incident.
Vance's assistant, Dr. Judith Mossman, will be portrayed by Michelle Forbes, most famous for her role as Ensign Ro on Star Trek: The Next Generation
Vance's daughter, Alyx, will be voiced by unknown actress Merle Dandridge. British actor Jim French will play Father Grigori, a booby-trap-happy priest who helps Gordon through the streets of City 17.
Dr. Wallace Breen, mysterious and evil leader of the humans collaborating with City 17's alien invaders, will be played by Robert Culp of I Spy fame. The alien slaves known as Vortigaunt will all be voiced by Oscar-winner Lou Gossett, Jr., who previously played a throaty alien in the 1985 sci-fi thriller Enemy Mine.

There's also some info on the size of hl2 in the Half-Life 2 fallout Forums which reveals an interesting fact, there will be a version DoD on the source engine, while this doesn't suprise me too much, I'd not seen it confirmed anywhere before.