In what looks like a pretty interesting collaboration between what was the LGA Group and YouGov, YouChoose is an online budget simulator that:

encourages members of the public to consider where council budget cuts should fall, where efficiencies might be made, and where income might be generated.

You can see  a working version up and running for the London Borough of Redbridge, and a PDF document describes the detail in more detail (the tool is free, but decent analysis of the data is going to cost you).

I’ve not really got a view on participatory budgeting, or whether YouChoose does it well or not. Anyone with a clue want to share their thoughts?