Google is the best I've found, but I considered it a high point in my Spanish learning when I started to stump the machine. (eg, I would put in "Mi padre es un taco pollo" and get out "I would like ketchup on that, sir!"... okay, not that phrase exactly of course, but a totally different meaning out of it than what I put in.) As said before, of course, there is no substitute for learning a language. For a quick word or two, or making sure that you're saying stallion instead of hair in your essay about horses, a quick run through Google Translate isn't bad.