Several options
Depends exactly what you want and what coverage you need.
The ever-popular Navbox ProPlan allows a GPS input and has comprehensive database, so if you want a vector based map that covers the whole of Europe that is a good choice.
MemoryMap will also take a GPS input and display your position on whatever map you have, including the official CAA charts in the UK (but no other aviation information). You could do the same with OziExplorer if you scan your own maps I suppose, but for the money you might as well get the proper charts.
I believe AnywhereMap are now making a PC version of their PocketPC software. They've always had a flight planner, which isn't much cop. Also, it isn't great for use in the UK because the database is poor.
From memory I think that AirPlan (which is cheap and functional if a bit ugly) will take a GPS input too and it has a pretty good global database.