Since Struts does not deal with or dictate the data layer, (DAO, etc), you are free to choose whatever you like.

iBatis

• http://ibatis.apache.org/javadownloads.html – iBatis website
  

Some iBatis tutorials, related to Struts:

• http://www.learntechnology.net/struts-ibatis.do – Using Struts with iBatis
• http://www.learntechnology.net/struts-spring-ibatis.do – Using Struts with iBatis and Spring
• http://ibatis.apache.org/javadownloads.html – Download and analyze JPetStore application, it is written with iBatis/Struts by iBatis developers