Black Uhuru - Unless you are going to get into the dub side of their catalog, the "Liberation: The Island Anthology" would probably take care of you. For a single disc (and a better taste of their dub stuff than what the anthology above gives you), check out their "Guess Who's Coming to Dinner."
Israel Vibration - Another group that has two sides to their catalog, regular releases, and dub versions. If you look them up on allmusic, the ratings are pretty accurate. Personal faves are "Strength of My Life," and "On the Rock." For their dub stuff, "Dub Vibration."
If your system has a sub, make sure it eats a hearty breakfast.
Mike