I'm sorry to tell you that, unless the albums are incredibly rare, they'll be worth next to nothing. The Sinatra one you mentioned is currently being auctioned on eBay - with just over 10 minutes to go, there are no bids and the starting price is 99p:
http://cgi.ebay.co.uk...f87398b#ht_500wt_1154
There are certainly some people who collect vinyl, but more for its own sake than the quality of the sound. I have the above album on vinyl in pretty good condition, but the remastered CD version released a couple of years ago walks all over the vinyl original in terms of warmth and quality of sound - just wonderful!
eBay can sometimes be a bit deceptive because often people auction their stuff there with very little notion of how much it's really worth, and unscrupulous dealers and collectors can make a killing.
Best idea is to Google the album's catalogue numbers...