The Congressional Budget Office reported recently on its comparison of a cap-and-trade program to a carbon tax program. The one-line conclusion is that carbon taxes are cheaper and simpler, but caps give more certainty.
For a lengthy and detailed commentary supporting taxes, check out Common Tragedies. Environmental Economics supports a cap on pragmatic, political grounds but also seems to set up the strawman that economists prefer the status quo over a system of caps! Felix Salmon is persuaded by the uncertainty of a taxation system to support caps.