It looks like Buildcraft has an automatic crafting table. You can even feed it and empty it with hoppers and chests, or pipes,, to further automate it.
If you want "standard bukkit server" without any mods required clientside, that would not work. For a mod to do that, it would require the client to have the mod as well. However, this would be achievable by means of a Bukkit Plugin. I don't know how to program bukkit though.
I see. I don't know how to do this (I'm pretty much a noob at mods making) but I'm sure someone has made a mod to auto recipe fill. Take a look around; I'll have a look myself.
EDIT: Download NEI, whether for 1.6 or 1.7 (for 1.7 go to Skydaz and run the installer, it adds compatibility for 1.7 but potions are unusable). Set NEI to recipe or utility mode, and left click the item in your inventory sidebar to open the recipe. Shift left click the ? button, and it should fill it.
Other than space conservation, is there any reason you'd want to turn your melon slices into melons? Unless you have a mod, melons don't give 9 slices when you break them down again.
EDIT: Download NEI, whether for 1.6 or 1.7 (for 1.7 go to Skydaz and run the installer, it adds compatibility for 1.7 but potions are unusable). Set NEI to recipe or utility mode, and left click the item in your inventory sidebar to open the recipe. Shift left click the ? button, and it should fill it.