Astrophysical "unitised" version of the Gravitational constant
Useful formulations which have taken some time to dig out:

$G\sim{4.3\times{10^{-6}}}\,\mathrm{kpc}\,\mathrm{M}_{\odot}^{-1}\,\mathrm{km}^{2}\,\mathrm{s}^{-2}$

or 

$G\sim{4.3\times{10^{-3}}}\,\mathrm{pc}\,\mathrm{M}_{\odot}^{-1}\,\mathrm{km}^{2}\,\mathrm{s}^{-2}$