Programmed Test Sources, or PTS, makes an assortment of nice frequency synthesizers.
I picked up a PTS 250, a 1 to 250 MHz synthesizer that came with no documentation. Mine had front-panel knobs with a resolution down to 1 Hz. Using these controls was intuitive, but I did some searching for information on how to use the remote programming connector on the back of the device.
I was contacted by a person from PTS. Material previously posted here was in violation of their copyrights. I have therefore removed the technical content about using PTS Synthesizers. My appologies to PTS and their people. Seems Agilent's laissez-faire attitude toward sharing of user manuals, or their content, is not shared by PTS.
I must now suggest that if you are shopping for an older instrument and would like to know more about it than can be guessed from knobs or connectors, you might do better to look for something like an HP 8662A.