The lighter block lights on fire when power is applied to it.
According to the Block and Item IDs spoiler, the Lighter currently has block ID 131, but it had block ID 112 when this Mod Compatibility List was published in January, 2011.
This video from March 12, 2011 shows Lighter blocks in use:
Minecraft- spider spawner trap with on/off switch
Mojang recently declared that plugins (mods) cannot have exclusive features, so it's no problem that other mods have blocks with similar functionality to the Lighter, such as the Hibachi in Better Than Wolves or RedPower 2's Igniter.
Mojang issued its statement so that it may freely implement functionality in Minecraft that is similar to that found in a mod. Indeed, Mojang has already done this with the Piston, Ender Chest, Anvil (Better Than Wolves has long had an anvil), and 3D Items.
[Updated Dec. 21, 2012 to add the Anvil and 3D items to the list of mod ideas that Mojang has incorporated into Minecraft.]