Trello, Quora, IFTTT, and Splitwise all appear to be offline, as are websites built with the site-creation service Wix; GroupMe seems to be unable to load assets (The Verge's own image system, which relies on Amazon, is also down); and Alexa is struggling to stay online, too. Nest's app was unable to connect to thermostats and other devices for a period of time as well.
Isitdownrightnow.com also appears to be down as a result of the outage.
Amazon has suffered brief outages before that have knocked offline services including Instagram, Vine, and IMDb. There don't appear to be any truly huge names impacted by this outage so far, but as always, its effects are widespread due to just how many services — especially smaller ones — rely on Amazon.
There's no estimate on when service will be restored, but Amazon says it is "actively working on remediating the issue."