Show prices, but make sure there is a good spread in the prices, so you don't pin yourself down as "cheap" or "high-end".
On the low end you can have standard, non-negotiable packages.
On the high end I guess you do custom projects? If some of your existing customers would permit this, then perhaps write up a case study on some of the larger projects you have done, and publish the price of these projects. Otherwise make up illustrative project descriptions for what you'd like to to, i.e. an abstract description of a typical high-end project for you, and suggest a ballpark figure for the price of such a project.
This advice goes against the grain; most consultants do not show prices on their webpages. I believe this is to keep upwards price negotiation power, i.e. to not lock oneself into a lower price bracket if the customer was willing to pay more. This is a real concern -- but attracting customers is also important, and I believe you will attract more customers with clear up-front pricing.
When prices aren't listed, customers assume the price is high. "If you have to ask, you can't afford it."
If you're an expensive boutique development company, that's fine. If you're trying to position yourself as affordable, prove it by showing your low prices.
+1 on Jesper as well, especially about how you could offer affordable packages but also say you do custom work. It's OK to not quote prices on "custom."