new Version (for Google Chrome users only, at the moment) gpxviz2
plot altitude profiles of your gpx files and save them as images.
analyze the slope of your tracks online.
hover over the profile to see details.
select parts of your track to get a detailed image.
(click and drag a section)
It is nessessary that your gpx file contain some elevation data in order to draw a altitude profile (look for "ele" tags in your file).