So I just stumbled upon a couple of Minecraft mods that I am going to have to check out. One is called Sonic Ether's Unbelievable Shaders (via pcgamer.com )which (as the name implies) adds lighting effects that look pretty damned good. There is also apparently a mod called Minerraira (Minecraft wiki via Pcgamer.com) which adds features from Terraria in to Minecraft. Never played Terraria, so i'd have to take it at it's word.
Check out the video for Unbelievable Shaders to see how it looks: