Not sure if this has been mentioned yet, but I recently did some testing and found that Blizzard has servers in 4 Datacenters in the US.
This post lists the IP addresses of all the realms. I thought it was a bit odd that they'd post this information, but I suppose anyone could get it if they wanted to connect to every realm.
If I looked them up correctly, the list goes like this
206.* - Boston
12.* - Los Angeles
63.* - Dallas
72.* - Seattle
If you are willing to transfer to improve your ping, it would be worth using the link I posted, and trying a realm at each location. In my case, I live in Alberta, and I play on a Dallas realm most of the time, and my ping is ~200. LA realms my ping is ~<100. Seattle for some reason is ~200 aswell, bad routing I guess. Hope this helps.