Try ebay or Discogs. Before you do this, check out the Frequently Asked Questions at http://www.78rpm.com/. Under "What Are My Records Worth", you'll find that the answer is between 10 and 50 cents each for the post-World War II stuff that you seem to have. Then you'll know that you should probably donate all or most of them to a thrift store that will take them or a friend or acquaintance that's fascinated by them.
In general, don't expect to create a lot of excitement trying to sell yet another bunch of Frank Sinatra and Bing Crosby records. I'm not saying that there's no one at all interested in those, but so many of these are still around (they sold millions of copies) that serious collectors usually own all the Franks and Bings they need. I got all of mine for free.
Too Many Records , Too Little Time Member since Jan 2013 306 Points
Without knowing the country of the OP it is a bit difficult to tell who wants to dip their hands in their pockets. But what is interesting is that (until recently) spotify and other sites were quite missing early and early Post War Bing and Sinatra recordings, particulary where they were less credited and singing with other bands. I would suggest that recording the records to CD or similar media is worth doing. Maybe someone might take them off your hands, and the label variations can be interesting for the database, but value, with smaller houses and a declining number of people aware of the performers let alone having time to be interested, go work it out. I will almost certainly have to let my collection go for very little in the next 10 years, (once I have finished adding to it from my neighbours discards)