I know of one called supriyosen.net. I used it when I first started to learn Bangla. I have been studying for almost a year now. It is very resourceful. Sadly, it will be hard to find Bangla learning tools online. I suggest investing in William Radice's Teach Your Self Bengali series. You can often find it dirt cheap on Amazon.com. I use this currently and it has helped me with the grammar. I am familiar with most Bengali grammar. If you would like my help feel free to message me

There are many links (not really great, however manageable) where one can learn the bengali language. You can find some of such sites smartly using appropriate keywords. You can find this link which has a collection of few websites. The link is: http://www.ats-group.net/learning/language-learn-bengali.html. Hope this helps.