new liberty standard was another
bitmarket.eu
bitomat
then mtgox
then bitcoinica
then btc-e
then others followed
I would add Bitstamp which was founded in 2011.
It is less than one year after MtGox, but what sets them apart is that they are still operational. They are now the longest-running cryptocurrency exchange, after everything we've seen with other exchanges, it's a real feat.
I would also point out Kraken dates from 2011 and is still healthy and doing well. I thought they were the oldest survivor, but maybe Bitstamp has them beat?
EDIT: Never mind, the wikipedia page on Kraken states that while it came into being as an entity in 2011, the exchange did not open until Sept. 2013.
topic is about BEFORE MTGox.. meaning its not a topic to mention every single exchange
but as OGNasty reminded me.. IRC was a good place to trade way from CEX even during early MTGox days