Your first port of call should be the official FreeBSD hardware compatibility list: http://www.freebsd.org/doc/en/books/faq/hardware.html

I am currently using a Draytek Vigor 120 modem (in full bridge mode) with FreeBSD (pfSense) and it has been running perfectly forever (current uptime is only eleven days but that was due to something unrelated) and I'd wholeheartedly recommend that configuration option.