Eventually I plan to have more detailed information about lightsabers and components here, but for now, just a brief note about how lightsabers (and items in general) are handled in the game. The SW:TOR equipment modification system went through an enormous amount of change at the end of beta, so we are still figuring out how things work now that the game is live.
Star Wars: The Old Republic uses a color-coded system of item quality that will be very familiar to players of World of Warcraft:
Gray: Cheap (Low Quality)
Higher levels of quality will have better stats for the same level, and will usually be rarer, more expensive, or harder to get. Higher quality items will tend to have more modification slots. Low Quality items are useful mainly for selling to vendors for cash, and there is a Companion function ("Sell Items") that allows your active companion to vendor these Low Quality items for you. Legacy items appear to be similar to Heirlooms (Bind to Account items) in WoW; in other words, they are items that can be handed down to other characters on the same account.
Some (not all) items in SW:TOR have a variable number of modification sockets, a bit like gem sockets in World of Warcraft, or rune slots in Diablo II. Certain components can be fitted into these sockets for stat boosts. Previously in beta, Premium and Prototype items could have a variety of socket types, including "Mod" components created by Cybertech, and "Enhancement" components created by Artifice. Lightsabers and Blasters also had Color Crystal sockets for special mods that changed the color of the blade or beam. Now, however, the modification system has been overhauled, and most Premium and Prototype items do not have mod sockets.
A new class of item has been introduced, called Custom items, that are "fully moddable"; that is, in addition to Mod and Enhancement sockets, they have a "base" component socket which can increase the level and basic damage/protection of the item, in addition to bonus attributes. This base component is called a "Hilt" for a lightsaber, or a "Barrel" for a ranged weapon, or an "Armoring" for a piece of armor.
There are still Premium items in the game that have modification sockets (Kira's lightsaber, for one, is Premium but still fully moddable), so there are exceptions to this rule.
Artifact quality items are said to be "partially moddable." It's not clear exactly what this means, but it does seem that the Base mod and Color Crystal sockets, if they exist, are "locked down," and any components placed in them can't be removed. It seems likely that Artifact items still have Mod and Enhancement sockets, but it's not clear how these work now.
Possible types of modifications that an item may have are:
Mod: A stat-boosting component created
Hilt/Barrel/Armoring: A level-changing core component normally only on Custom items, created by the craft for the item type
Enhancement: A stat-boosting component created by Artifice
Color Crystal: Weapons may have this slot which changes the color of the blade/beam and adds small stat boosts
Augment: A special component slot for items crafted by a Critical Success; components created by Slicing
In theory, it is possible for a crit-crafted weapon to have all five socket types (though I have not yet seen one).
In earlier beta versions, lightsabers had more specifically-named socket types (emitter matrices, power crystals, focus lenses, etc.) similar to the KOTOR assembly system, but these have been replaced by the more generic "Mod" and "Enhancement" sockets.
As of a recent beta build (11/25), it appears that lightsabers can be crafted by Artifice but only at max level (the new lightsaber schematics require Artifice skill 400), so prior to that all lightsabers must be acquired through quest rewards, gear drops, vendors and the like. Artifice can construct the Hilt, Color Crystal and Enhancement components, and Cybertech can construct the Mod components.
For those using two lightsabers (such as Sentinels), they are two different items, one for each hand.
In addition to whatever stats are attached to a Color Crystal, this component type also actually changes the color of the lightsaber blade. So far a number of color variations have been seen, including blue, green, yellow, purple, red, orange, and white. The color crystal that comes with a pre-order is black with a yellow glow. Other colors reputed to exist are: cyan, magenta, black-blue, and black-red.
There are Force alignment restrictions for colors traditionally used by the Sith and Jedi. Red crystal are unusable by anyone with a Light alignment, and green or blue crystals are unusable by anyone with a Dark alignment ranking. If you maintain a neutral alignment (which is very difficult), you can use any color you like. The colors other than red, blue and green have no restrictions (as far as I've seen).
Currently there are only two known types of lightsaber: the normal lightsaber (used two-handed or one in each hand), and the double-bladed lightsaber (as used by Darth Maul). There is a "saberstaff" which is mentioned in the proficiency description for the Shadow AC, but this appears to be another name for the double-bladed lightsaber. Only the Shadow AC of the Consular class is currently allowed to use the double-bladed lightsaber or the saberstaff.
In SW:TOR, there are no "two-handed weapons," so unless you are actually using two weapons, you can also equip an off-hand item such as a Force focus or a personal shield generator... even if you are using a double-bladed lightsaber. The ability to equip most offhand items appears to be gained at level 10, and according to the Advanced Class you choose at that time.
There are also apparently offhand-only lightsabers and other melee weapons.