modding games and editing games?

Hi when i get my pc fixed im contemplating gettinga game where its got a good modding community. ive tried a few games with specially modding communitys but i havnt had much luck finding any i like. the ones ive tried are:

Half life 2

gta SA

oblivion morrowind

I chose these as ive got a low pc spec and wondering is there any more out there thats suitable for low end spec modding?

and are there anygood games that can run on low spec computers?

Many thanks

well i was looking for a more of a creative game and designing games like the sims but i dont think it will run on my pc if i bought it.

Source and 1.6 both have the biggest modding communities out there, you can be running away from a horde of zombies, hiding behind a giant can of soup, or surfing all while playing the source/half-life engines, counter strike is the best.