529 Plans appear more complicated than they really are. First of all they are set up by states, so pretty much every state has one or more plans. WA has one, called GET and it's pretty lame.
The general rules with 529 Plans are that you can live in any state, get a plan from any other state and then use the proceeds for a school in any third state. Some plans require you be a resident, but most don't.
The key thing with choosing a plan is making sure it managed by a reputable firm with a good investment track record and that the investment strategy is adapted to fit the age of the child as she/he nears college age (i.e. reducing risk over time).
I ended up choosing Michigan's plan because it has an excellent track record over 1/3/5 years. Is managed by TIAA-CREF, has a very low fee structure (less than most), is easily transferable to other plans/states if desired (haven't tried that yet), and provides flexible/small minimum contributions which can be easily set up on a monthly basis if desired.