My ISP recently recommended the following tool (DMT - http://dmt.mhilfe.de/) for obtaining a detailed anaylsis of my phone line. There are several version available depending on which DSL modem you are using. I managed to find a version that works with my LinkSys modem even though it isn't mentioned in the list of supported modems. Unfortunately the forum pages for the application are all in german so deciphering the results is a bit tricky. I've included a screen capture below:

I'd be intrested in comparing results with others, and comments from anyone who knows how to interpret the graphs above.
Cheers,
Dean