Hello,
I have got a 640 GMAT score. But my full-time work experience is 6 months and continuing ( as a independent working insurance agent). I am confused to apply for which B-schools due to less work experience.Please reply asap.

Until you have three years' work experience you are limited to:
a] MA and MS programmes at good schools
b] MBAs at bad schools.

For US schools, read http://www.find-mba.com/board/23411

Elsewhere read http://rankings.ft.com/businessschoolrankings/masters-in-management-2012

please suggest any universities which are possible for me to enter with this background.

There are lots of universities on those lists.

I highly recommend you do one of the following:

1. Work for another two years and work on your GMAT score to get it closer to 700. At this point you'd be competitive at an MBA program that would be worth the investment.

2. Pursue a ranked masters in management program instead of an MBA. There are a lot of these, mainly in the UK or Europe. Examples of schools that have masters in management programs that you can look into (make sure you check the entry requirements):

Bath
Mannheim
Copenhagen
Aston offers a range of MSc programs
Grenoble

thank you