Josh Orton lays out pretty well the issue of "congressional insider trading." Short version: Congressional staffer knows what goodies are in a bill being voted on in the middle of the night, leaks it to someone on the outside, they make a killing on the stock market.
It's technically legal if there are no kickbacks involved, although it rather defies belief that if this is widespread activity that there wouldn't be kickbacks.
Obviously this should be against Congressional rules and against the law, but more than that it's something the financial industry should be up in arms about. While it does allow a small minority to make a quick buck, they're making it at the expense of everyone else in the biz. They're getting hosed and they should be pissed.