keep in mind that normally they list dynamic contrast ratios. also keep in mind typically whether this is grey to grey, black to white, etc are not listed. also keep in mind that this number can vary from firm to firm testing the same tv.
generally speaking plasma televisions have much better contrast ratios then lcd (led tvs are still lcd) however, plasma televisions have their own set of issues.
go see the tvs in person and make the judgement with your own eyes. if the contrast looks good to you then go for something in that range. remember, contrast ratios are not the only important thing to consider.
your best bet is to search for reviews of a tv you're looking for to find the actual contrast ratio after the TV was professionaly calibrated. Like ssdx said companies advertise dynamic contrast ratios which for all intents and purposes are made up numbers of nothing. You want to find real world numbers which unfortunately for LED/LCD unless you get yourself an elite black pro the contrast ratio isn't gonna be all that great.