Google Translate and Bing Translator are two of the most popular translation websites; both allow you to translate English into various languages. Other online translation services include Linguee and WordLens.
Google Translate is a simple online translation service that allows you to enter English words, sentences or paragraphs, and instantly translate them into dozens of other languages. You can also translate from other languages into English. Google Translate automatically recognizes the language you enter, so you can translate foreign text into English even if you don't know what language it's in. Translate tweets or entire websites into English with Google Chrome's in-browser auto-translate feature.
Bing Translator has most of the same features as Google Translate, but also supports spoken words for some features, and allows users to upload and translate entire documents and provide feedback on the accuracy of each translation.
Linguee doesn't translate entire documents or websites, but does allow you to see other uses of a word or phrase from around the Web, which may help you better understand the meaning and context of a word, especially if you're trying to learn English or another language.
WordLens is an Android and iPhone app that translates photographed text; this is useful if you need to quickly translate street signs, menus or other offline text.