RouterStats was one of the first programs that made it easy to monitor your line stats. Initially designed to work with the Netgear DG834 series, it has since expanded to work with several other routers, although you may need to do some slight configuring yourself.

RouterStats can monitor Sync speed, SNR Margin and 2 other user defined graphs of your choice such as attenuation or errors. 

Features: Access Telnet data Line stats & other telnet data Customisable graphs Daily graphs saved as .jpg Monitors & Graphs: SNR Margin Connection Speed 2 User Defined Options Bit loading & Bit swaps

Routers known to work with:-
Netgear DG834 series, DG2000, DGN2000,  Thomson ST585, TG582n, TG587n.  Also Belkin F5D7630-4A, D-link DSL502-T,DSL-504-T, Draytek Vigor 2600G, Linksys HG200, WAG54G, WAG160N, WAG200G, WAG354G + more