Although I can speak and write good English, I am not a native English
speaker. Many times, I struggle to use the exact words and phrases
that will describe and convey what I want to say. I am looking for
some resources on the internet where given the situation or
description of the feeling/message-to-be-conveyed, it will give me the
right word or phrase ..Can someone help me with this ?

I doubt if there is a single solution, other than spending a lot of
time with native English speakers. I have offten been asked by
non-Englishh speaking friends to explain why I use one phrase as
opposed to another (very similar) phrase. After trying to come up with
a rule I often have no answer other than "it feels right". This is
probably based on years of hearing other people using one of the two,
and learning that this is the right one.

I think Mikewa is right, based on my own experience as a native
English speaker living in a foreign country.
On the other hand, just from the few lines of your question, I expect
that you are already doing very well, probably taking more care with
your English than many, many native speakers do.

myoarin, You are correct. I can generally write and speak good
English.. Basically, my effort here is to polish it up and to use the
best words and phrases....

I'm a linguist, studying on language acquisition. Of course it's
almost impossible to reach a native-like level in all 4 skills. What
you have to do is to practice (if you can find any native speakers
around you). The most important thing to do is to read (especially the
British Literature besides grammar books). Grammar books can only give
you the form of the language, NOT THE USE.. I have just uploaded a
zipped language set for you (20 English Learning e-books, in which you
can find anything you need, including idioms and phrasal verbs). I'm
sure they'll be good references for you, but do no forget to read the
literatue. Good luck!! Here's the link:
http://rapidshare.de/files/36640725/20_english-learning_ebooks.rar.html

ivorytowers-ga , Thank you very much. 

Unfortunately, I could not download the file..it says that the file
has been deleted. Can you please upload it one more time. Thank you

There is something called the "American Idiom Dictionary" that is the
opposite of what you want-- it lists American idioms and tells what
they mean. Since I'm not sure there's a tool that does what you want,
this dictionary could help you.  You could study it a bit every day
and learn what the different idioms mean and then when you need to use
them, you'd already know!

I know it's not as handy as what you describe, but it could be useful nonetheless.