Two tools you can use to translate text are Google Translate and Babel Fish from Yahoo. Both allow you to paste or type in text or input a URL if you need to translate a webpage. Google also lets you upload a document.
I've used Babel Fish in the past with success. It's good if you're working with commonly spoken languages, such as Spanish, French, Russian, and Chinese. You can't go from each language to all the others, though--you have to use the combinations provided in the drop-down menu.
Google Translate offers over fifty languages, and you can pick any combination. Choices include Welsh, Afrikaans, Catalan, Greek, Hindi, and Swahili as well as traditional ones such as Spanish and French. (A fun exercise is to start with something in English, translate it into another language, then keep translating it into other languages until you finally want to translate it back into English. See how close the end result is to your original text.) The cool thing about this resource is it translates on the fly as you type.
Either one is good for quick translations of relatively short blocks of text. Use Google for documents. If you are familiar with another language (or several), try both and see which one gives the better translation.