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

My first Note :) ...

I don't know what exactly i'm(I'm) going to write here... but(never start a sentence in English with this word)i (I) think i (I) should start writing to improve my English... In(When) writing and speaking in(unesscessary word) English i (I)get too confused it seems i'm making mistake(It seems like I'm making mistakes) my pronunciation is not correct... well, i'm (I'm)going to write about my yesterday's exam today... (Well today I am going to write about yesterday's exam.)
Exam is nothing but a tension. (Exams are nothing, but irritation.)yesterday(Yesterday )I seated for an exam . I was tensed(I was tense), because I did not completely read all the three sheets provided by our teacher. We are three friends decided to complete our syllabus by dividing three sheets among three of us, because we always maintain our seat plan serially.(My friends and I decided to complete our syllabus by diving the three sheets amongst ourselves. We are usually serious about our seating arrangement.) At the beginning of my exam, I was moving forward and back and that is why I got the the concentration of the madam. At first, she warns me then second time she took my paper and she told the rest of the students "see all of you who are trying to make move your body or making noise, I will also take your paper too. I was lucky, she gave back my papers within two minutes. After   finishing my exam I felt free for the day. Marks does not matter but tension is the great matter...(Marks don't matter, but the tension is a problem.)

*Your writting is pretty good. Your punctuation and sentence structure can be a little off sometimes but  it's ok. I make mistakes when writing term papers and compostions all the time.