Protrader 20th floor in the merc, has a retail branch, but no prop.
Andover has a branch called Maverick Trading, but I don't know the address or #
Ext used to be there, but was bought by Point direx about 2 weeks ago
Onsite trading, 19th floor in the merc
Tradescape in the chicago stock exchange building.
There are literally hundreds of 2 to 10 people prop groups, but to find them you'll have to run around the merc and ask questions