From Bali, Aceh Aid Bucket Brigade blog details the type of  skills that can be used on site:

Indonesian Language (essential)
Medical
Nursing
First Aid (wilderness/disaster first aid, not pre-hospital first aid, these people won't get to hospitals)
Rescue and Evacuation
Emergency Sanitation (as in refugee camps, devastated/recovering villages)
Water Purification / Clean Water Systems

Also, they can use some technical help too

We are encountering some "desk work" that take up time we could be using to get medical supplies on planes, get relief workers into the field, coordinate with NGOs, etc. Things that don't need to be done here. I mean work that could be "outsourced" to "virtual volunteers" (you?), such as updating our distribution list, and fixing it, making a database compiled from forms filled out by people applying as volunteers, maintaining specific lists, solving software problems by IM and email . . . .

We are doing lots of very important things here, that not many people in the world can do . . . in a language that most of you reading this will never need to learn to speak . . . so I think our time is crucial here on the ground in Indonesia . . .