Good RMI books
"java.rmi" by Esmond Pitt & Kathleen McNiff - you'll have to get this used off amazon since its out of print I think. ISBN 0-201-70043-3
"Java RMI" by William Grosso - from O'Reilly. haven't used it as much as the other, but it seems pretty good. Still in print I think, but buy it used and save money. ISBN 1-56592-452-5
this post - Michael hasn't done it yet (I don't think) but there's been talk of him turning the post into the start of a book. Its a good primer with some depth to it.
HTH
Chris