The Sharpless catalog of emission nebulae contains 313 entries representing H-II emission nebulae with a declination of -27 degrees or above. Compiled and published by American astronomer Stewart Sharpless (USNO) in 1959 (see here), the catalog contains a wide variety of star formation regions across the Milky Way including various Herbig-Haro and Wolf-Rayet objects as well as a number of well-known emission nebulae such as the Trifid (M20), the Eagle (M20), Orion (M42), Lagoon (M8), the Crescent (NGC 6888), and the Crab (M1) nebula.

Note: The impressive crescent-shaped emission nebula Sh2-188 in Cassiopeia happens to also be a planetary nebula. Lying in the immediate vicinity of Ruchbah (δ-Cyg, mag 2.65), Sh2-188 is characterized as an ancient planetary nebula lying appoximately 850 light-years away and with most estimates citing an age between 20,000 and 25,000 years old. As indicated by the image below, the nebula is asymmetric in brightness with the more pronounced nebulosity being observed to the southeast. This asymmetricity is believed to be the result of bow shocks involving the interstellar medium and the planetary nebula itself (see Wareing et al). More specifically, the brighter portion of the planetary nebula visible in the image below represents the interaction of the nebula meeting up against the interstellar medium while the former is moving through space at approximately 125 km/sec and with approximately two-thirds of the original mass already left behind and "downstream" (opposite side of the planetary nebula's bright crescent). The actual apparent diameter of the planetary nebula is estimated to be 15 arc-minutes and spanning 2.8 pc (9.1 light-yrs) across (aggressive non-linear stretching of the image below does indeed reveal the extended ring structure of Sh2-188, virtually identical to Figure 2 in the Wareing paper, and which is only hinted at in the version below). The central star (mag 17.4) associated with Sh2-188 is marked in the second (H-a) image below.