As far as I know, there is no simple, quick way to check bisulfite conversion. But bisulfite sequencing using automated ABI or similar platforms could give better and reproducible results compared to manual bisulfite sequencing.
The first link is a PLoS paper in which different bisulfite conversion kits are compared, not only concerning conversion efficiency, but also many other factors. They use Sanger seq of a cloned PCR product to asses conversion efficiency, which is probably the method you will most likely be able to use (guessing your lab equip by your message, others may be possible too.). Don't know how "quick" the method has to be, but a few days should be enough for this. Primers etc are given in the paper. Message here if this is not what you wanted and I will look out some other methods, if you like.
The second link is not about conversion method, but it gives a nice colleciton of useful information on bisulfite-treated DNA in general, like quantitation, quality assessment, primer design etc. Stuff that it good to know if your are doing research using bisulfite-treated DNA.
I am using mouse neuronal cells for conversion and wanted to check for efficency. Can some one give me the sequence for the over and under conversion oligos.