I use a CTX AD-1970 monitor for that kind of thing. That is not its real model number. It's a slapped on number because the monitor was modified by some other company to lower its sync rate capabilities down to 15 KHz. It can handle all Amiga modes, and the controls on the front have enough adjustment in them so that none of the modes suffer from the "black borders" problem that others do, like the Commodore multisyncs.
