There are several stock exchanges around the world, catering for many different companies. The following is a list of some of them that you may find useful:
London Stock Exchangehttp://www.londonstockexchange.com
NASDAQ Stock Markethttp://www.nasdaq.com
New York Stock Exchangehttp://www.nyse.com
American Stock Exchangehttp://www.amex.com
Toronto Stock Exchangehttp://www.tse.com
Copenhagen Stock Exchangehttp://www.xcse.dk
Stock Exchange of Hong Konghttp://www.sehk.com.hk
New Zealand Stock Exchangehttp://www.nzse.co.nz
Swiss Stock Exchangehttp://www.swx.ch