There are two ideal exams after completing SCJP viz SCWCD and SCEA.
Which exam to take next depends on your experience of J2EE.
SCEA exam covers architectural topics like UML, design patterns etc.
This would be a good choice if you have a good knowledge of J2EE including Servlets, JSP.
If you want to clear your JSP, Servlet concepts then SCWCD would be a good choice.