I’d go with proven Java servlet servers: Jetty or Resin. The have both been extended to handle WebSockets:
Jetty WebSockets
Resin WebSockets
My personal choice would be Jetty, as it’s very simple to use and I’ve been using it as embedded server in several projects.
There are also some new kids on the block like Atmosphere and jWebSocket, but for servers I prefer to go with a proven solution. Jetty and Resin are also generic Servlet servers, so you can go with one product for all your serving needs.