Bubble Blaster HY 5000 is the replacement with the closest flow rate. I doubt that is will perform any better - it might last longer but Coralvue pumps don't have reps for lasting much longer than the Sedra. The sedra pump, while people might think that they are old and worthless, had a really good air/water ratio and were quite effective. You can get 2 Sedra 5000s for the cost of a Bubble Blaster. Just sayin'.
DC skimmer pumps, like Diablo and the same design, are a joke IMO - most of the people that I have ever met that love them either have little other experience with a good skimmer or grow excess waterborne bacteria with organic carbon creating an environment in which even a sea clone can produce good skimmate. I would not recommend them to anybody. Some people really love them, but I have not seen it personally.
I used a Tunze Hydrofoamer with good results on a G3, but I don't know if they make a pump big enough for the G4.