Marine Chart, from EarthNC - not bad.

Transas - a bit too simple, not a real chartplotter.

INavX - my favourite, from the same people as the MacENC I have for N American waters.

Plan2Nav - a big disappointment, I'd expected better from C-Map. It crashes frequently.

However, I see that more are coming out. There is now a Navionics app, which just might be worth looking at.