The book I'm reading now is java.rmi: The Remote Method Invocation Guide. The authors are Esmond Pitt and Kathleen McNiff. So far I have found it well laid out and clearly written. The example code is a bit light, but adding a little imagination should do the trick.
I have yet to find an online tutorial that I really like. Then again, distributed program writing is difficult and it involves thinking your way through some interesting problems patiently. For me, web tutorials don't really offer that. They all seem to assume some familiarity with distributed programming. That's a pretty big assumption.
The best examples I see for RMI have been in books on Jini. Look for some intro to Jini tutorials; that's realyl a pretty good start.
This forum is actually a makeover of the RMI/CORBA forum, which I requested so we could throw Jini, Jiro, JXTA and other aspects of distributed Java programming into one place. We've just posted a Jiro book review, and we'll have one on the book java.rmi book soon too. I'm hoping we can shake things up a bit in this forum.
It'll also give me a good excuse to look into CORBA/IIOP which until now I haven't given much thought.
Tell all your friends!
------------------
Michael Ernest, co-author of:
The Complete Java 2 Certification Study Guide