On many recent Sun platforms, the component serial numbers are available from the prtfru command. Sometimes on the system controller or ILOM Iif the system has one) there are commands like showfru...
This was true in 2003 when it was posted.
In 2008, quite a few of the newer Sun machines do report the chassis serial number in the output of prtdiag -v ; generally at the end.
explorer is s Sun Service tool for collecting system configuration information about your machine. It is very useful when you need to open a service request with Sun.
If you save the explorer...
Sneep has been updated to find the serial number on many of the more recent platforms which have "hardware" support for the chassis (product) serial.
( Unfortunately, that does not include the...
iostat -E is great for getting the serial number of the individual drives, but sometimes (like to place a service call on a storage array) you need the serial number of the overall storage unit.
...