It comes down to your business model and types of services you offer. If you offer "widget" type services then I would recommend putting prices on the site.

If you don't offer widget services (commoditized services) or you offer more custom services in addition... I personally would not list prices for anything that needs a conversation to determine what the client needs and your time / effort involved.

Not only does this help you scope before offering a quote, but it also screens out potential clients that need custom service but want to treat you like a widget.