Earlier quoted context omitted.
Still seems to be very little. You can get some boxes that convert adsl to ethernet (ATM over ethernet or whatever standard your country uses) that basically have no config and connect those to a router.
That's how I did it, connected my WRT-54GL (Tomato) to a D-Link modem/router, works fantastically well.
I used to do this until something happened at my ISP and my router can no longer authenticate against my ISP's PPPoE server. Now I have my modem providing NAT and DHCP, and my router is just a dumb access point. The only problem is my modem has an externally accessible administration page running on port 4567, and telnet on port 1111 that I can't turn off, even when all remote management configuration options are turned off. I've had to set up a cronscript to attempt to telnet into the thing continuously, and if successful it will kill the httpd server and telnet daemon.
It's absolutely ridiculous how insecure home network equipment is.