As I often mention when folks start talking about WebSphere (or any vendor-specific) certifications, the first thing I always recommend is to take a look at which ones will most benefit you. Which ones will most help with your current employer or with potential future ones?
There's a few IBM tests that are fairly generic - 484 (Enterprise Connectivity with J2EE 1.3), 486 (OOAD with UML) and 141 (XML and Related Technologies) - that will help with almost any situation. Beyond that, there's the question of whether you want to take the administration-type exams or the development tool exams.
But I hope that least helps you start to answer the question you've posed.
Theodore Jonathan Casser
SCJP/SCSNI/SCBCD/SCWCD/SCDJWS/SCMAD/SCEA/MCTS/MCPD... and so many more letters than you can shake a stick at!