Favorite video game Mod?

Personally I'd have to go for Jailbreak which I was introduced to in the UT and UT2004 games.
http://www.moddb.com/mods/ut-jailbreak

I <3 Day of Defeat. A lot of Valve stuff also comes to mind.

Whoa, epicly large video.

Sven co-op has given me the most fun.

Insurgency
The Hidden
Red Orchestra

Mods are incredibly overrated. 

The great oblivion mods too many to name

Favorite game mod?  Nude <Insert Game Title Here> Mod

Actually, it's Auctioneer.  Not terribly flashy but extremely useful to those in the know.

The Hegemony mod for mount and blade

I remember playing counter strike with the "CS for kids" mod that was in the xanatos video. That was fun.

Sweet half life,peaces like us,and They hunger.

MB

Garry's Mod

And tons of the mods you could find for that.

Strangelove

They Hunger for Half - Life was about the only one I bothered to play.

is82 for Battlefield 1942...good times.

Team fortress 2 . Its a mod of Halflife

The original Team Fortress for Quake.  Nothing else comes close.

Insurgency.
And i also have high expectations for Black Mesa Source if it ever comes out.

Used to play this a lot, it didn't get much support though.

I downloaded many Scource mods.. I played alot of Zombie Master and was admin on one of the most popular servers but in the end other games came out and I never went back to it. Sometimes play Garry's mod and things like that.

Some old Unreal Tournament and Quake 2 mods. I don't remember what ones they were though.

Some Counter-Strike mods were kind of fun too.

The Haunted mod for UT3, it kinda like an okay version of Resident Evil 5 mixed with Left 4 Dead with a lot of fun weapons to use.