http://dictionary.reference.com/translate/
This one is better than wordlingo or babel fish. I have been taking beginner's Italian so I have a VERY basic foundation of Italian grammar and usage, let me emphasize BASIC.

This web site is pretty good to use in conjunction with that kind of foundation. However, like the other posters said, it will not pick up nuances in the language and will translate everything word by word, rather than taking into account the entire sentence structure. I think if you totally rely on one of these programs you can make a big mess, that could be pretty funny or embarrassing. Also you have to know how to phrase things in English so they come out right in Italian when you type them into the translator. For example, I was writing, I know what you are saying. To make it translate better, I have to type in English, I know that which you say. Oh, and also, the translators do not seem to distinguish between "you" formal, familiar, singular and plural. When you type in "you", it seems to conjugate everything as voi (you plural).
This is more work, but I suggest buying the dictionary that wldspirit recommended and then read Italian for Dummies. It is an excellent book with basic grammar and is easy to understand. Believe it or not, I can now read Italian and get the sense of the letter, although by no means can I translate the letter word for word.