You need to look at "Trade exchanges", not just "Exchanges".
Trade Exchange = To make offers (bid/ask) or (buy/sell) {You set the rate you desire, as an "order"}
Exchange = To get an exchange, at a specified exchange-rate that the exchange has offered.
Here are a few "Trade exchanges" and "Exchanges", otherwise known as "Markets"...
(Look under the markets menu on top.)
http://bitcoinwisdom.com/Thanks for the link. I know the difference, but many sites don't make it clear exactly what they do.