Lonely Planet's website is quite good for letting you know if you need a visa for a certain country or not.
http://www.lonelyplanet.com/

But it's always best to check with the countries own website as some countries you will require a visa before you arrive there or sometimes you can get them on arrival.

Also if you have an older passpord you may require a visa before you arrive in the country if you passport is not machine readable.

Remember that Visa requirements can change quite quickly.