For any dictionary, make sure you check all the meanings of words!
Leo is the most respected and useful dictionary for students of German.
pons.eu is also great.
Other good dictionaries:
At your own risk, translators. These translators may seem like lifesavers, but use them with caution!
The only grammar site you will ever need! Everything from verbs to adjective endings to nouns. Its great!
Lingo Fox is a great website to conjugate verbs. Type in the verb and it will give you all the tenses and participles.
Podcasts auf Deutsch!
Listening to German is one of the best ways to learn. There are several podcasts out there that are pretty easy to follow and help your German tremendously. Here are a couple examples, you can find many more on itunes by changing the country to Germany at the bottom of the itunes store page and selecting podcasts. All are free!
Slow German – a great podcast for students in the German 200-300 level. The German is very clear and, as the name states, spoken slowly. The topics vary, many have to do with German culture.
Schlaflos in München – spoken at a normal speed but is very clear. It is a good resource for students of German 300 and above.
Tagesschau – a German news program. The German is very clear and easy to follow.