David J Frew, Q A Parker and I S Bojicic from the Hong Kong university recently published an article called
The Hα surface brightness–radius relation: a robust statistical distance indicator for planetary nebulae
Measuring the distances to Galactic planetary nebulae (PNe) has been an intractable problem for many decades. We have now established a robust optical statistical distance indicator, the Hα surface brightness–radius or
SHα–
r relation, which addresses this problem.
http://mnras.oxfordjournals.org/cont.../1459.abstract
Table A4 in supporting information gives distances.