Form ID

is a object property assigned by creators or engine to each and every thing in Fallout 3, be that items, NPCs or parts of world like sign on a wall or the wall itself.

Base ID (aka Actor Base parameter in the game console)
Base ID is the number assigned to template of each object that is used to create many instances of that object. For example all bottle caps in the game have exactly the same Base ID. This ID is used in scripts or console with commands that create new instances of object, like  or.

This value is also used for the setessential command, which makes the NPC invulnerable. To use it, put in:

Reference ID (aka ObjectReferenceID in the game console)
Every new created item have its own reference ID. For example, all the bottle caps created from same Base ID will have different reference ID. This ID is used to manipulate existing objects with commands like,  , or  , for example.

Any item that is not created by pre-defined game scripts (either original or from mods) will have reference ID starting with FF to indicate that this item belongs to this particular save game. It is for dynamically generated items, like loot from containers, random encounters or trader's wares.

The following is the list of Reference ID for a lot of characters in the game (I think all of them). The "generic" units are probably useless, since the game spawns them, but for the named NPCs, you can use various commands to either go to them, resurrect them, or warp them to you.