I am the author of Gmap4 which is a 100% free no-ads full-screen enhanced Google Map viewer. It includes detailed topographic maps (courtesy of www.mytopo.com) for the USA and Canada. Gmap4 runs entirely online. There is nothing to buy, nothing to download, nothing to install.

In addition to surfing topographic maps, you can also view data from the following types of files: GPX, KML, KMZ, TPO & Google MyMap files.

You do need to place your GPX, KML, KMZ and TPO files online before they can be displayed by Gmap4. The easiest/fastest way to place files online is via Google Sites (free). Don't be shy. You will find hand-holding-step-by-step instructions in the Gmap4 Help file.

Here is the general recipe for building a URL to display a data file with Gmap4 (do not include the quotes, these are not real links):
For data files showing locations in the USA or Canada:
'http://www.mappingsupport.com/p/gmap4.php?t=t2&q=http://url_to_your_file'
For data files showing other locations:
'http://www.mappingsupport.com/p/gmap4.php?q=http://url_to_your_file'

Below is a link to the Gmap4 homepage. Check out the 'Examples' button and the Quick Start section of the 'Help' file.
http://www.mappingsupport.com/p/gmap4.html

Finally, if you run a website where people file trip reports you could consider allowing Gmap4 to run in an iframe. Your users could include a 100% free interactive map with their GPS track and waypoints along with the rest of their trip report. Gmap4 has a liquid design and will look decent in an iframe down to 400px by 400px. For examples: Search the Trip Report forum at http://www.nwhikers.net for 'Gmap4'.

Enjoy,
Joseph