A while ago I found out that the D-Link router I had (655), had some XML output available for DHCP Lease status and interface statistics. I also noticed that these stats only became available after logging in initially from a certain IP/MAC (no session state kept). The router gives a salt that is valid for a while and on the client side that salt is used together with the password to generate a hash which is used to login. You can then proceed to retrieve the XML data.

In case anyone is interested, the (very hacky) scripts are on Github: https://github.com/michielappelman/router-stats