Go with a cloud hosting provider that has greater bandwidth then the hackers that are attempting to bring down the service with a DDos attack. As an example in the recent wikileaks DDos attempts, the hackers called off their attempt to shutdown Amazon because they could not exceed the bandwidth/resources that Amazon possessed. There is nothing you can do about a DDos attack by a nation-state simply because only another nation-state would have the resources to counter them.
Ramsey-After thinking about this and considering all options there is a way to do it yourself if you had the resources. There is not a full need to go with hosted cloud solutions. If you have multiple branches in different physical locations you are just as strong as these big guys. Since each of your locations have different Public IP’s and most likely different ISP’s a ddos attack would have to flood and attack each of your ISP’s. With the different Public IP’s as long as you are monitoring your traffic and have backup Cloud Base at another location you just close the one that is being attacked and bring up the other to Master at your other physical location. Bam! That is the answer!