If you know what country/countries your coins are from, and don't mind descriptions in German, you could try this online catalog of 20c world coins:
http://www.inkoze.de/index.html?/linkswelt.htmlFirst you click on a letter to get to a list of country names that start with that letter; then you click the country name. These PDF files are from an older (1999) version of the Schön catalog of world coins. Note that the prices are still in DM; divide by two and you get the approximate value in € or $. The current version of the Schön catalog is, like pretty much any other coin catalog, not available online.
But if you can get that "Standard Catalog of World Coins" at a library nearby, that would actually be easier. Partly because it's in English, and also because the coins are primarily sorted by face value.
Christian