Well, how's Halo 2?
I'm pretty sure the Silver package also has HL: Source. Let me go check the differences.
*fires up Steam and waits for the obligatory update*
OK, the Silver package has all the same games as the Gold one, and its only $60. The additional $30 for Gold buys you some Valve goodies/merchandise (well to me its all junk, but some people dig this shit).
Oh also, having purchased retail HL2 in a store, I can't recommend you do the same. The standard box only includes HL2 and CS: Source. Get it off Steam, if you want a CD make your own. The DVD/CD editions are also irritating because they demand a disc to play CS: Source. There may eventually be a way around it. Maybe Daemon Tools will support it in a new version, although that's not really a solution to me :/
I've been told I can just upgrade and get HL: Source and DOD: Source later, but I haven't had the cash to test that theory yet. I can tell you that CS:S is just more of the same with new models and pretty textures. I'll probably be sick of getting shot in the head within the week. But HL2 is pretty fun.