Best Games to put Mods.

TES games, Fallout 3, Just Cause 2, etc. Just sandboxes in general.

Minecraft and Skyrim a bit.

edit: Very minor things with Skyrim tbh.

Half-Life
Halif-Life 2
Portal
Amnesia

minecraft and beth games

Well, Gothic (1 and 2), L4D2, TES (Skyrim and Oblivion), Mount & Blade: Warband, Minecraft and minor mods to The Witcher.

Garry's mod!

I wonder why no one talk about Medievel totalwar 2,Rome TOtalwar, Paradox stragery game like Heart of iron 3, .....etc. Homeworld 2 also have a nice collection of mod too

The GTA games, Just Cause 2, Left 4 Dead 2, Killing Floor. And that's from the top of my head.

STALKER series
Half-Life
Half-Life 2
Portal
Amnesia
Fallout 3 and NV
Oblivion and Morrowind
Lots of other games

Hmmm, Counter Strike Source, L4D2, Just Cause 2, And Minecraft i suppose?

I like to use mods allmost every game i play, and i play a lot.
So here is some good, moddable games:
Skyrim

HL2 series

HL1

Arma2

Arma3

Borderlands 1 & 2

Call of duty series

Cs 1.6

Css

Cs:Go

Crysis series

Gmod

Gta series

Just cause 2

Killing Floor

Left 4 Dead 1 & 2

Mafia 2

Stalker series

Serious sam series

I don't make mods, but I use a ton of them in Scribblenauts Unlimited (if those on Workshop are considered mods). I've also used a couple of mods on L4D2, like replacing the jockey-riding-you sound effect with the Benny Hill theme song, and the charger yelling "THIS IS SPAAAAARRRRRTTTTAAA!!!" when it attacks, among others.

Amnesia!

Fallout 3 and New Vegas.

Torchlight 2.

Skyrim and Oblivion.

Dragon Age.

Minecraft is the obvious answer... the game itself has several mods built into it including how it saves the map.

Left 4 dead 2, only one button to install any mod :>

Valve games.