You can open up a demo account with thinkorswim for free, and you'll get access to Level 2 data for free. I don't have much experience with other brokers, so I don't know how the quality of thinkorswim's data compares to others'.
i have ToS, i tried it with them, and their market depth data is very very minimal. when i asked them if they have more, they said no, and that you would have to go another broker (when i looked at their market depth, it only went out a little ways), im looking for like the full market depth or out a long ways, am i doing something wrong there or is it just that limited?
Maybe MB Trading would work? http://www.elitetrader.com/vb/showthread.php?threadid=188644#post2708304