I love my Korg MA-30 metronome, especially for the shuffle rhythm, an earphone jack when I don't want to annoy the people around me (more than my harp playing already does...), and a nice visual screen. Well worth the $30 (especially since it was a gift :-)
I've got a JamMan looper and it has a metronome with a volume control that can be adjusted to "plenty loud", it records and can play back instantly. For reasons unknown to me, it also seems to reduce feedback since I can crank up the volume louder than without it. A nice tool for learning.
Peace and music, Dave
-- Carter