There are SO many websites that offer great price guides it just requires a little looking. Also there are collectors books. You can find them in book stores or places like ebay or Amazon.
The best source to determine coin values is using The Official Red Book United States Coins by R. S. Yeoman. The value of your coins will depend greatly on their condition, date of mintage, and scarcity. The guide book will explain how you determine the quality of the coins.
If you are talking about US coins, head to your local library and ask for a book called United States Coins 2009 or 2010. It is also known as "The Red Book. " You could also check an active coin web forum like PCGS or NGC.
There are many websites online that you can go to and enter your coin information and it will tell you what the coin is worth today. You can also take it to a coin specialist so they can give you a relative value of the coin(s).
Visit the local Public Library and consult the numismatic section. Look for specialized catalogs as "CoinManage 2009" and literature as 'Coin Collecting For Dummies. ' Those are good books to start.