MarinePure, followed by live rock. ^_^ I mean nothing beats live rock given that it also acts as deco, and base for coral and stuff. But MarinePure is great to let you not have as much rock as you think you'd need. One day I want to set up an aquarium with MarinePure 100% replacing live rock. XD
Poly-filter is also great. I like it because you can kinda tell is anything bad is happening. I have a piece in the back chamber just in case anything goes wrong, though it barely change color from white, so that's a good thing.
A filter sock is also great to just catch particles and help clear up a tank a lot.
Algae scrubbers are also awesome, especially because well, algae grows so easily, and just offers such a great way to soak up nutrients. Best thing (at least for mine) is that it will adapt as needed and shift between hair algae, cyano, etc. presumably depending on what nutrient is elevated at the point in time.