Solutions to the lack of code transparency in economics?
You need the journals...

Nothing will move without it. The American Economics Review has taken the lead in requiring all data papers to make their data and source code available. Unfortunately, there's no real indication that other journals will follow suit, despite the formidable reputation of AER. Sadly, even the AER doesn't have a clear repository and not all code is available even though they require it of the authors.

Beyond that, David Card has a nice repository of sorts for structural econometrics data. Josh Angrist and David Autor should be praised for creating Data Archives that document their own work. But at this point it's still up to individuals to make their research transparent and their code available.

For what it's worth, I've been thinking about this issue a lot lately and decided to create a Google Code Project where economists can upload their code:
http://code.google.com/p/econ-code/ ... That said, I have not yet tried to publicize it and think the ultimate key to adoption lies with the journals.