Stated from PlanetHalfLife who talked to Valve. This is the purchase option you can do:
"Retail Boxes:
Standard Edition - includes HL2 and CS:Source. Ships on six CDs, in one of three box-art packages (Gordon, Alyx or the G-Man).
Collector's Edition includes Half-Life 2, Counter-Strike: Source, Half-Life 1: Source, a Half-Life 2 T-shirt and a Prima book sampler. Ships on a single DVD.
Steam Packages:
Bronze - HL2* and CS:Source.
Silver - HL2*, Counter-Strike: Source, Half-Life 1: Source*, Day of Defeat:
Source*, Valve's back catalog currently available on Steam.
Gold - HL2*, Counter-Strike: Source, Half-Life 1: Source*, Day of Defeat: Source*, Valve's back catalog currently available on Steam, Complete Strategy Guide from Prima Games, 3 different Half-Life 2 posters, Half-Life 2 hat, Half-Life 2 postcard, Half-Life 2 stickers, Half-Life 2 Soundtrack CD, Chance to win a trip to Valve! (1 trip offered for every 5000 Gold packages purchased).
*To be made available upon product's release.
Pricing details are expected to follow shortly. In the meantime, it looks as if the appetite of Half-Life nation will soon be sated! Planet Half-Life will keep you up-to-date as soon as more information is released."
Also. Counter Strike Source is going to be released next week, when it comes out the beta will be closed.
For anybody who has a ATI HL2 voucher, you will get an automatically get the Bronze package from Steam.