In the UK (and probaly other countries), one can use a program called Memory Map which includes detailed Ordnance Survey maps of just about every area of the country in high detail, coupled with aerial maps too. It's good for hiking/camping/rambling/ambling/climbing/boating/cycling/off roading etc.
'Draw' a route on the map on your PC, fly through it in 3D to check it out, transfer it to your PDA, take it with you, use it, edit it to account for reality etc. Find out more here:
http://www.memory-map.co.uk/pda_mobile.htm. I have no commercial connection with this product, just think it's good.
PS
Just seen someone else mentioned MM too. Also, I don't know if JotM is talking about MM, but MM's fly-throughs are self-contained and can be on a 3D map or a 3D rendering of aerial photos. They can also be saved to an avi file.