chores appropriate for a three year old?

My three year old is starting to become a bit obstinate and not paying attention to me. She used to help if I asked, and now she openly tells me that she can't do things because she doesn't want to, is sick, doesn't have to etc. She just turned three and I assume this is all very natural. But I want to make sure she develops a work ethic. Are chores in order now? What would be appropriate for a three year old? Should money be involved at all, or at what age?

thx!