lingro is a free multilingual AJAX dictionary and language learning site. Currently supporting English (ESL), Spanish, Italian, French, and German.
Dictionary in one click ! Amazing tool!!! Just enter the URL of the page you are going to read , select the kind of dictionary you need , click on the word (s) hard to you...and ...voila!! Instant translation or explanation on the same screen!!!
You can also download your own files and click on the words you want translated. (Right hand side top - file viewer)