I believe the most reliable is the Origo Sztaki online dictionary. http://szotar.sztaki.hu/ The website itself is not available in English, but just select "angol ---> magyar" (English ---> Hungarian) in the dropdown menu. The only (major) drawback, however, is that this dictionary is more suitable for learning English than Hungarian. There are example sentences for the usage of an English word, whereas Hungarian words don't have them. Also, it gives only the basic (dictionary) form of a Hungarian word. After thinking it over and doing a Google search, it is advised to learn each Hungarian word (noun) in this way: út (basic / nominative) utat (with accusative suffix -t) utak (plural suffix -k) útja (possessive form) I could not find a reliable online dictionary providing these four forms.

This one is a really useful and versatile site with dictionary and example sentences. http://en.bab.la/ If you are a Windows Phone user this is definitely the best offline app. (However it has built-in online dictionary as well. http://www.windowsphone.com/hu-hu/store/app/magyar-szótár/9e3fc4ff-d523-4d9c-8dd3-fa1ef99d12d5 Good luck!

Sztaki definitely works, and is the one that I use the most, but I would definitely suggest picking up a printed dictionary if you can. They are simply so much more reliable in the translations, and include more examples of use and variety. They're well worth the money.