Well, it depends on what you mean by fine grain, and what you want out of the film.
The majority of the super fine grain developers are high solvent developers. For instance, my gut reaction to "fine grain" would be perceptol or microdol. D76 stock would fit, too. However, not only are those all powder, but they also cost you quite a bit of speed. There isn't much point in shooting TMZ if you have to shoot it at like 560 or 640 (TMZ is really an 800 or so speed film by ISO standards, so getting it to look normal in a speed-decreasing developer will bring you in even below that).
So, the question becomes which of the speed-enhancing developers will give you good speed but less grain. If you want liquid, I'd try DDX as a first stab. That's some pretty good stuff and while it's less solvent than D76, it is still technically a solvent developer.
allan