Replicant, perhaps? http://www.replicant.us/

But without the proprietary drivers, not much of the hardware will be functioning. No GPS, no 3D acceleration and no hardware video codecs.

I don't mind the proprietary drivers and firmwares. (Actually, I do, but I'm realistic and know that the completely open source phone won't happen ever, so I just accepted it.) What I'm after is stock AOSP (with binary blobs, if no other options exists), with root access, and without the proprietary Google apps (not because of their proprietary nature, but because they are of absolutely no use to me, I'm happy with the open source equivalents). Replicant tries to clone the proprietary bits, but that's not what I'm after.

I'm only after convenience. As I said, I can compile AOSP, but I don't want to invest in this maintenance work at all. I just want a plain Android that can update itself. Basically the only thing I'm after is OTA updates to stock AOSP. I don't care about modifications, new features, or more free drivers. If such a project ever appears, I'll be the first to donate. I would even pay for a subscription to such a service.

That is what CyanogenMod is... AOSP (+drivers) with a few tweaks/addons (that can be disabled), root, no Gapps, and gets OTA updates.

There are some ROMs out there that are closer to AOSP but normally have limited phone support and no OTA updates.

I doubt anyone would go to the trouble of creating a Android ROM for different phones and not tweak anything on it.

AOSP doesn't include drivers so you meant to say stock Android builds.

I mean AOSP plus drivers, but without the proprietary apps like Google Chrome, Play, Maps, etc. The stock Android builds do include these apps (please correct me if I am wrong).

But what I really am after is not some build of Android, but the service that enables OTA updates to this build of Android. I'd even pay for such a service.

You are right, I misspoke... "Stock Android" includes the Gapps.