Related to Bulk activate product keys in Steam, I have the same problem with a lot of bundles (Humble Bundle is no longer a problem, but other sources have given me a crap ton of Steam codes that are tedious to redeem one at a time). In addition, redeeming a key automatically wants to start downloading the damn thing which I often don't want to do. Is it possible to add a key to Steam without needing to download it right away?
I want to have all the games I own on Steam, but I don't necessarily want to download them yet (or maybe ever). I have a problem now with keys scattered across various sources that I forget even which games I actually own!
Edit: Messing around with this it appears that @Lyrical is correct. There is no option to "not download", but you can cancel out before the download starts. One you get to this point, the game is added to your library:
But you can't actually cancel here (note cancel is greyed out), instead you have to hit "next" and then here:
You can actually hit cancel.