Also you can buy them from reputed book stores world wide. Those who need translation from English to Tamil or Tamil to English will need a dictionary according to your work. It may be Tamil to English or English to Tamil dictionary.
Also there are special dictionaries for each subject as Physics, Chemistry, IT and many other subjects. There are electronic dictionaries which are available freely in the market. They are in CD or downloadable files from web sites for computer based programs and hand held ones which can be carried in the shirt pockets.
Some of them are offering how to pronounce the English world easily. These products can very easily search and find the required word. Some models have already translated big sentences in Tamil and English for translation purpose along with word to word translations.
Here you can find some online Tamil dictionaries for your reference.
If you have any of your own work or good one in the public web send it to firstname.lastname@example.org.