How can I fix bad elevation data in a GPS log? Lately I have been doing my bike rides with a GPS logger, and its elevation recording is extremely erratic and thus unusable. Please see:

http://gpsloglabs.com/share/d9393bc6c20b8b0debfe26234169be632eb019e0/

You can see from the altitude contour that it does some measurement, but it is too jerky, and thus my total climb is way too big.

How can I work around this problem? Is there any service that will 'flatten' my trip to an accurate topographical map and correct the altitude data?
Try http://www.gpsvisualizer.com. In the parameters set "Add DEM elevation data" to "From best available source". This will replace the recorded elevation with elevation data from a database, which should be more accurate.

Edit: Try this other sub-page of the same site to upload your .gpx and then download the fixed .gpx
http://www.gpsvisualizer.com/elevation