Hi Trulia :),
The impulse answer is to do a short sale. However, to do a short sale, you must have a "hardship". A few examples of hardship are medical expenses, reduced income, and having to move for a job. Having to move for a job can be within the Seattle area, if the job requires an extra long commute that puts a "hardship" on you.
If you are moving up to a larger home, it might even be strategically smart to bring cash to closing, so you can close and buy the more expensive home. The reason this can work to your benefit is because if houses are appreciating at 10% annually, the $300,000 home goes up $30,000 and the $500,000 home goes up $50,000.
Each situation will require specific analysis. If neither of the above two options work for you, you stay in your current home until it appreciates enough for you to have positive equity. You may want to see if you fit one of the refinancing programs, so you can get your interest rate down to today's still record low rates.