CRS has released Campaign Finance Policy After Citizens United v. Federal Election Commission: Issues and Options for Congress by R. Sam Garrett.
The short paper also makes reference to CRS Report R41045, The Constitutionality of Regulating Corporate Expenditures: A Brief Analysis of the Supreme Court Ruling in Citizens United v. FEC, by L. Paige Whitaker. If anyone has a link to a posted copy of that report, please pass it on.
UPDATE: You can find an unformatted version of the CRS report here. Thanks to two readers for the link.