What meaningful financial regulation should we advocate?

I've heard many leaders say our focus should be about "Main Street instead of Wall Street" or how policy should favor the "entrepreneur and not of the speculator" but those are just soundbites and I haven't seen any specifics.

I believe new regulations are needed and have put a lot of thought into specifics but would love to hear thoughts about specific changes we can make. I'm sure some of sloganeering will make it into this discussion but if you have any specific ideas for how to get there I'm very interested in hearing them.

For example, if you think we have a "fat cats on Wall Street" problem do you know of any specific ideas to do something about it?

Here are some thoughts going through my head:

I believe that deposit banks have a limit on how much of the market they can control. I have been procrastinating on looking up the specifics but I remember bank mergers having regulatory hurdles because of it. At the time I assumed (again, this is something I need to research quite a bit) that this is due to the danger to the economy of having a depository bank fail.

I wonder specifically if this (if it does in fact work the way I assume it does) should be made stricter and require even smaller banks. If this is not the way it works I wonder if it should.

The thing is, depository banks aren't at the center of this crisis, so that leads me to my next thought. Why not create federally insured lending with federal regulation. The way I see that working is that companies could choose to deal with a federally insured institution, and that the insurance would come with regulations limiting the amount of risk the lending institution would be able to incur. Specifically I would like to see them required to keep enough clean assets in relation to their loans to survive an uptick in default rates on the loans. I'd also be interested in codifying risk through credit ratings, and keep those who are willing to gamble on bad credit out of the insured system.

But that leads me to my next doubt, I'm not sure this should be voluntary. After all, if a big enough lender opts out but still goes under it can be in the public interest to intervene, even if they didn't opt into the regulation of risk.

Anyway, those are some examples of the thoughts I've had on it. I have a lot of other random ideas but am not yet happy enough with any of them. So do you have any ideas for specific changes we can make? Or have you heard of any good ones?