I have the Topo USA Version 3, it works great, I really like the 3-D map and then rotating it to look at it from different angles.

One thing I wish I could find again, last year I found an internet site with topo mapping with aerial mapping. You could find what you wanted on topo then click up aerial and could zoom in to the degree on being able to see trails. It made me think that if an elk were standing in a meadow that you could see it. But for the life of me I cann' t find it again. Perhaps its a paid sight now, donn' t know. If someone knows of a sight like this let me know.
Thanks
David/Mo