Eheim Professionel 3 250/G65/2071. Great design. The 250 is the current nomenclature. It just replaced the G65, which replaced the 2071.
Perfect for a 25, but ready for something larger as well, with no upgrade necessary. And you know you'll eventually want something bigger. This should take you from a 25, to a moderately stocked 55, with no other filters needed. Your mileage may vary.
I have a G160 & G90 on my 75. I cannot hear them, even with the stand doors wide open. These things are german quality, and almost dead silent.