Adaptive optics systems using sodium laser guide stars are widely employed at major astronomical observatories. It is natural to ask whether other atomic species might offer advantages. In this paper, we review all abundant atoms and ions in the upper atmosphere, including Na, Fe, M g + , S i + , C a + , and K and also the non-metallic species N, N + , O, and H, considering their potential for adaptive optics. Return fluxes for all transitions that can be excited using either one or two wavelengths were computed. We also considered multi-wavelength emission, comparing the performance of different transitions for polychromatic laser guide star (PLGS) adaptive optics. We find that of all the mesospheric metals, Na is the most suitable for both monochromatic laser guide stars and PLGSs, providing about six times more return flux than the best transitions in Fe. For high-altitude observatories, excitation at 330 nm in Na should give the highest PLGS performance. Atomic O, N, and N + have strong transitions and very high abundances in the mesosphere. This makes them potential candidates for the generation of intense laser guide stars by amplified spontaneous emission, if a suitable excitation process can be demonstrated. Direct excitation by CW lasers is impractical, as all transitions from the ground state are beyond the atmospheric cutoff. Nevertheless, it may be possible using high-power pulsed lasers.