The first thing I did when I began to learn Chinese was to search open-source softwares and free websites to help me. The commercial softwares are way too expensive, and the open-source solutions are very few...

Then I found nciku.
Nciku is the google of dictionaries : very clear and simple interface, but a lot of possibilities.

Nciku is an Chinese-English dictionary that accepts pinyin (with auto-completion), hanzi and even handwriting. The results show the hanzi and its pinyin, the definition and lots of examples. With the new text-to-speech option you can listen to the word you searched, and also to the examples!

Handwriting?

The fun part is that you can use handwriting! If you know how a Chinese dictionary works, you understand that it's a revolution. The handwriting recognition works perfectly, even if your hanzi looks like a 3-years old kid did it. No need to remember the radical, to know the stroke order...

If like me you are learning Chinese writing, you can easily find an unknown character and then get the stroke order!!

Sign-Up for more

If you sign-up, you can get your own vocabulary lists. You can do like me and list the words you can't remember. Make vocab list by themes. You can keep track of your progress and pass memorization tests.
I found it very useful to consolidate the vocabulary I learned during my Chinese lessons.

If you sign-up you can also participate to the BBS, Questions & Answers, grab conversations and personalize your Nciku.

Unlike many (Chinese) websites, it's free and "clean" : no annoying popup, no annoying mails, no ads, it works on Firefox, Opera, konqueror... Nckiu is easy to use, simple, but very complete.

The swiss army knife of Chinese dictionaries.