We need to store coverage areas and search by location over arbitrarily large areas. It has to be able to handle polar searches and coverage areas that span multiple hemispheres. No GIS can do this. Informix has the Geospatial Datablade, but it costs like a hundred grand. Does anyone use something more affordable--preferably free?
The best open-source and free geospatial database is in my opinion PostGIS. It is easy to use and has a huge support group (also for example at https://gis.stackexchange.com/)
It also connect to all sorts of different open-source programs and web-interfaces which should make data editing, viewing and sharing easy.
It can handle the date-line and the poles:
What about the date-line and the poles?
All the calculations have no conception of date-line or poles, the coordinates are spherical (longitude/latitude) so a shape that crosses the dateline is, from a calculation point of view, no different from any other shape.
I agree with Speissburger that PostGIS (an extension of Postgre) has excellent Geospatial support. In the open source world, this would also be my recommendation. (MySQL claims to have some geospatial support but it is very limited in capabilities)
For completeness, Microsoft's SQL Server also has good geospatial support - I think it was introduced as an extension to SQL Server 2008, and then standard after that. I have heard that Oracle also has good geospatial support, although I have never use it.