well. you should know that a lot of the old commons and uncommons won't be worth much. only a select few are worth anything at all.
and the same thing is true for most rares as well. only to a lesser extent. if you want to know what sells well. you can use the price guide at magic.tcgplayer.com
I find it to be fairly accurate and it uses ebay auctions as a guiding point for what a card is actually worth to people. in that respect its better than Scrye.
If you have a spare underground sea lemme know. id be happy to buy it off you at a fair price.