Are there any good guides on how to combat a DDOS? I'm curious how a team of good technical people without past experience in the area could react.
Your best bet is to move to a protected hosting provider (dragonara or ddoshostingsolutions are quite good for Europe / US). Failing that you can purchase a bunch of VPS servers, round-robin DNS to them and reverse proxy to your actual server (and keep that IP off the DNS system entirely). This way only the proxy servers will go down if you are attacked.
Edit: If they are not spoofing they sender address, you can achieve some success by mailing the hosting provider of the IP performing the attack. In 90% of cases the server has been hijacked and they will shut it down, this only works for US / European companies though since Chinese / Russian hosting providers never ever reply in my experience. For maximum success you can attach a tcpdump of the attack traffic.
Most of the cases though it's as simple as attack is 200 mbit and connection is 100mbit -> no amount of dropping packets once they reach the server will do anything, as the connection is entirely saturated.