What are your favorite modifications?

[Gundam Eclipse]

After playing Skyrim, I have been much more interested in mods than before. Mostly for Half Life, such as Earth's Special Forces(http://esforces.com/) or stuff like Advance Wars Frontline(http://www.moddb.com/mods/advance-wars-frontline) for C&C: Red Alert 3.
So yeah, my question would be, what are some of your recommended/favorite modifications? Game specific or total modifications, any kind at all.
In case you have no idea what kind of mods are out there, this might be a good site to check out:
http://www.moddb.com/

 

[Clarky]

dont know if it should be counted as a mod or a restoration but the resoration project on kotor 2 i love as it makes the plot a whole lot deeper

another mod for kotor 2 was a fan sequel called the jedi masters, while a little rough around the edges it had some good moments besides some silly story ideas

 

[chains_of_androm]

Vehicle mods for GTA series was pretty fun. Zombie mod for CSS was good too.

 

[Gahars]

The mods for Left 4 Dead (especially the voice and character swaps) are always fun. That's definitely worth a look if you have the game.

 

[Gundam Eclipse]

Bumping because I am fairly certain quite a few peeps will be interested in this
http://www.moddb.com/mods/merp-middle-earth-roleplaying-project
Looks like it has potential to me :V

 

[DaggerV]

That sounds like a fun project actually.

 

[the_randomizer]

Texture/vertex (character importing) and soundtrack mods for Super Smash Bros Brawl. Since I'm learning how to do all that, it makes it all the more exciting!

 

[DoubleeDee]

Any mod that can make you flyyyyy.