Geographic information Systems provide an automated way of displaying and interrogating our evidence. 

It requires that the data to be utilised has a spatial component.

Site specific data could be combined with Spatial data and  environmental data, to answer questions about relationships and flows between sites. Or positioning of sites to exploit natural resources.

With GIS we can also add a time dimension to our data, there by examining quickly changes in spatial relationships of our data through time.

Mapinfo and ArcView are two of the most popular and low priced GIS available (Around $3,000) Many Archaeological community have developed 'add ons' specifically to assist archaeologists.

Sydney University did have a particularly good web site outlining Archaeological projects that have used GIS, However the site is being replaced. It can be accessed here still. (Note it has not been update in some time)

Esri (ArcView) has a web site devoted to Archaeologists.