In my previous post i described about diposable Id in Yahoo.There is no such option in gmail.
but i found a way which works similler to Yahoo.As many bloggers already posted gmai ids can be edited by adding ‘+’ operator,ex: yourID+something@gmail.com is nothing but yourID@gmail.com.With the help of this i found a way in gmail.Give different ID where any forms ask for your ID,like below
Then go to your gmail & click on “Create Filter”

Fill the to email adress as you given in forms & create filter as you want……

Then you will see the emails in your inbox like this…..

Update:
Many forums are showing errors like “Invalid email ID” because of ‘+’ operator.So better use ‘.’
(DOT) operator instead.

Disposable Ids in Yahoo