^(http(?:s)?\:\/\/[a-zA-Z0-9]+(?:(?:\.|\-)[a-zA-Z0-9]+)+(?:\:\d+)?(?:\/[\w\-]+)*(?:\/?|\/\w+\.[a-zA-Z]{2,4}(?:\?[\w]+\=[\w\-]+)?)?(?:\&[\w]+\=[\w\-]+)*)$

##</code><code>##

Test URL:<br>
http://www.abc.com/test.pl?a=1234
http://www.abc.com/?a=1234

##</code><code>##

# @stephenhay (38 chars)
^(https?|ftp)://[^\s/$.?#].[^\s]*$

# @imme_emosol (54 chars)
(https?|ftp)://(-\.)?([^\s/?\.#-]+\.?)+(/[^\s]*)?$