  Motivated by integral field units (IFUs) on large ground telescopes and
proposals for ultraviolet-sensitive space telescopes to probe circumgalactic
medium (CGM) emission, we survey the most promising emission lines and how such
observations can inform our understanding of the CGM and its relation to galaxy
formation. We tie our emission estimates to both HST/COS absorption
measurements of ions around $z\approx 0.2$ Milky Way mass halos and models for
the density and temperature of gas. We also provide formulas that simplify
extending our estimates to other samples and physical scenarios. We find that
OIII 5007 A and NII 6583 A, which at fixed ionic column density are primarily
sensitive to the thermal pressure of the gas they inhabit, may be detectable
with KCWI and especially IFUs on 30 m telescopes out to half a virial radius.
OV 630 A and OVI $1032,1038$ A are perhaps the most promising ultraviolet
lines, with models predicting intensities $>100~\gamma$ cm$^{-2}$ s$^{-1}$
sr$^{-1}$ in the inner 100 kpc of Milky Way-like systems. A detection of OVI
would confirm the collisionally ionized picture and constrain the density
profile of the CGM. Other ultraviolet metal lines constrain the amount of gas
that is actively cooling and mixing. We find that CIII 978 A and CIV 1548 A may
be detectable if an appreciable fraction of the observed OVI column is
associated with mixing or cooling gas. H$\alpha$ emission within $100\;$kpc of
Milky Way-like galaxies is within reach of current IFUs even for the minimum
signal from ionizing background fluorescence, while Hydrogen $n>2$ Lyman-series
lines are too weak to be detectable.
