that would make steam 100% awesome!

No. You can only 'gift' new games or parts of special offers that you already own (like with the orange box) to people on steam.

Makes sense from a business standpoint (if you're Valve), but yeah, I wish I could give away or sell on my old games.

And unfortunately there can be no second-hand market (not even with a % of every sale going to Valve) on a digital platform, what with there not being any wear and tear on media carriers or key troubles.

well, Steam's refusal to honor the first sale doctrine is one of the things that pisses me off about Steam. Granted, most games are worthless after a year, but it'd be nice to be able to give them away or sell them. Destroying the second-hand gaming market is something all kinds of game companies would just love.