Do you need to sell to relocate to another job, or because you can no longer afford your current home?
If you need to relocate, you can:
1. Have your Realtor ask the lender(s) for a short sale package and see if they will be cooperative. You'll need to show that you are insolvent (cannot pay your bills).
2. You could offer to take back a promissory note for the short fall (not ideal, but an option)
3. Let the lenders foreclose (least desireable option).
4. Lease it out (talk with a CPA regarding tax consequences). Least impact on your credit and in a soft market common)
If you prefer to stay in your home, ask the lender(s) to consider restructuring your loan so the payments are manageable.
From the lender's perspective, they would prefer (in order)
1. You stay in the home, modify the loan
2. Short sale, they lost some money, but they will ask you to help (so if you have other assets...life insurance, 401 K, etc.).
3. Foreclosure - most expensive for the lender, not desired.