Marlin is a relatively new file browser for GNOME somewhat similar with Nautilus when it comes to features, but with a different default interface.
Zeitgeist (and Activity Journal - previously Gnome Activity Journal) is getting some amazing new features.
Nemo is a different kind of file browser. You can use it to browse files based on the date you last accessed them, in a calendar-like interface. So by using Nemo, you don't have to remember where you put it, but when!