i want to add urls in my reference

i am using the following code in my .tex file

    \bibitem{bl}Business Logic layer, \url{http://en.wikipedia.org/wiki/Business_logic_layer}, 23 12 2011.


however, i get the following output in my console

    ! Undefined control sequence.
{http://en.wikipedia.org/wiki/Bu...

?
! Missing $inserted. <inserted text>$
logic_layer}, 23 12 2011.
?
! Extra }, or forgotten \$.
, 23 12 2011.
?

! LaTeX Error: Command \item invalid in math mode.


whereas my .pdf file entry against this code is this.

    Business Logic layer,


what is this error about and how can i set this right?

-
Have you loaded the url package? – Seamus Jan 6 '12 at 8:58
Loading the hyperref should also work, i.e., make the command \url available. – Mico Jan 6 '12 at 9:02
@Mico that's because hyperref loads url – Seamus Jan 6 '12 at 9:16
i m a newbee with latex so trying to learn its tricks, many a times the "how to do this" is not that descriptive. thanx – Arifah Azhar Jan 6 '12 at 9:16

To use the command \url you need to load the url package by adding \usepackage{url} to your preamble.
Many packages (like hyperref) load url automatically.