hi Rob,
well, the generation of Unique ID depends a lot upon your application, you know. what kind of fields you have, what kind of other constraints you have. how you are going to use the Unique ID in your application etc....
but as far as i remember there isn't a direct way you can generate like GUID using some standard Java Class (please let me know if you don't know what GUID means) EXCEPT one RMI utility which uses IP address and an object reference unique across that IP address (across the JVM running on that machine).
look at,
java.rmi.server.ObjId for details.
i am not sure if this is useful to you because this depends upon IP address and in RMI the server is usually having Unique IP (please post more questions on RMI at Remote Objects forum on Javaranch as i 'm not at all a wizard of RMI. i just know little bit) but in your case it might not be applicable you know.
just my 2 cents.
maulin