I need a sublet for 5-6 months in New York. While there are mamy
listings in Craiglist, they do not provide as much information as
listings in paid sites like sublet.com or Rent Direct.

However the latter need a registeration fee. I dont mind paying this
fee, but want to do it only for one site.

I would like to find information on what are the most popular sites
where ownersand current renters put ther apartments up for subletting.
Some articles and/or reviews to back up claim would be helpful.

Having been on both sides of the equation (as both somebody looking
for a place to live and as somebody looking for a subletter to
temporarily take my place), the best advice I can offer you is: The
"best" website for finding sublets in NYC is the one which actually
gets you a sublet. If this sounds like a truism, it is intended to be.
You will not know a "best" site by looking at it or through rankings,
because it doesn't exist. The only way to find a good sublet is to
either do all the footwork on your own, and pursue every avenue that
you can think of, or to spend exorbitant amounts of money on a service
which will find you a sublet according to your specifications.

You also haven't stated whether you're looking for a luxury-style
sublet suitable for a financial executive or a college-student
dormitory. These will affect the type of website that would interest
you. Judging from the amount you've paid for this question, I'd guess
that you probably want the latter more than the former.

In terms of how I found a subletter: I used Craigslist, some local
community boards and mailing lists (both electronic and physical), and
put up posters in buildings similar to my own. I also told everybody I
knew on planet Earth what I was looking for. This last method proved
to be the most useful, when after 2 months of searching, I was almost
ready to throw in the towel before my friend called me and hooked me
up with somebody she knew.

/ephraim

Ephraim is clearly the voice of experience, and offers some excellent
advice. His point-of-view, however, is of someone already in New York
City. I have the feeling that you may not be in NYC now, and are doing
this subletting from a distance?
He's on the money in asking about the price range you are working
within. At one end of the price range is the tons of "corporate"
sublets in NYC, with abundant amenties and high rates. A good place
online to look into those is www.homestore.com.
One suggestion I have for you in the category of non-corporate sublets
is the Village Voice weekly newspaper's classified. They have 47
sublets listed, last I looked, and seem to post new listings
frequently. Go to: http://www.villagevoice.com/classifieds/index2.php.
Hope this helps.
scribe-ga

The NY Times has also has sublets listed in their online classifieds. 
The SUNDAY real estate section is the best. But it actually goes
online on FRIDAY NIGHTS at MIDNIGHT.

Another source, but you'll need connections, is the "wanted" and
"Sublet" bulletin boards at Actor's Equity and SAG (The Screen Actor's
GUild) in NY.
I don't know if they have online boards, and if they do, you'd need to
be a member or borrow somebody's membership #.   Same for
posting/reading in Manhattan in the actual Equity or SAG offices.  But
I know people who managed to get in there and found places to rent and
sublet, since actors are always going out on the road.

I know people who have also found sublets by searching NYU bulletin
boards and Columbia University bulletin boards . . .not sure if there
are online equivalents for them, but it's easy to find out.