With Android 6.0 Marshmallow officially out in the open and the factory images having already been posted, all that's left to do is wait for the over-the-air updates to hit devices, and for the OTA downloads to pop up for people to install manually instead of waiting. For the most part installing the OTA downloads manually is much the same as flashing the factory image, so users will simply need to pick their poison and go that route. If timing is a factor, then the factory images are a better solution as they're already up and available for the list of supported devices that were confirmed to get it, which includes the Nexus 5, Nexus 6, Nexus 7 2013 models, Nexus 9, and the Nexus Player.
As for the OTA downloads, not all of them are available yet but they are starting to come down the wire with at least two links available so far, and those are the Nexus 7 2013 LTE model, and the Nexus 9 LTE model. There's still nothing for the WiFi only models of either the Nexus 7 2013 or the Nexus 9, nor the Nexus Player, Nexus 5 and the Nexus 6. Once again though, the factory images are available for all the Nexus devices which were confirmed to get Android 6.0 Marshmallow updates.
There's no telling how long it could take for the OTA download links to show up for each individual device, but chances are it won't be much longer than this week in general. Having said that, we'll have all the OTA downloads listed below by device type with the associated links to download the OTA installation files. If you're unsure of how to install OTA downloads manually, your best bet is to wait for the OTA to come to your device on its own. If you're eager to flash the factory images because you don't care to wait whether for the OTA to hit your device or for the OTA download files to show up, you can follow this guide from earlier detailing how to do so.
Nexus 7 2013 WiFi Only: Android 6.0 Marshmallow OTA
Nexus 7 2013 LTE: Android 6.0 Marshmallow OTA
Nexus 5: Android 6.0 Marshmallow OTA
Nexus 6: Android 6.0 Marshmallow OTA
Nexus 6 AT&T: Soon!
Nexus 6 T-Mobile: Android 6.0 Marshmallow OTA
Nexus 6 Project Fi: Soon!
Nexus 9 WiFi Only: Android 6.0 Marshmallow OTA
Nexus 9 LTE: Android 6.0 Marshmallow OTA
Nexus Player: Android 6.0 Marshmallow OTA