A small subset of AGNs exhibit extremely broad, double-peaked Balmer lines in their spectra. The profiles of these lines are reminiscent of emission from an accretion disk at a characteristic distance of a few hundred to a few thousand gravitational radii from the central supermassive black hole. The hosts of these line profiles (the “double-peaked emitters”) also share a number of extreme spectroscopic properties that set them apart from typical quasars and AGNs. These properties can be explained in the context of a model of a thin accretion disk, illuminated from a central, hot, vertically extended structure. As such, the double-peaked emission lines provide us with a direct view of the outer parts of AGN accretion disks. Moreover, because of their extreme properties, double-peaked emitters can teach us general lessons about all AGNs, that we could not otherwise learn from the average quasar. In particular, I will describe how we can (a) glean the structure of the broad-emission line gas and its connection to the accretion flow via UV spectroscopy, and (b) how we can study dynamical phenomena in AGN accretion disks by monitoring the variations of double-peaked emission lines over very long time scales.