A bettercorruption model would definitely be No.1 on my list. I now always play a basic mod I made in the editor, with lower corruption and a higher optimum number of cities. Sure, distance and rank corruption do help tone down the runaway civ effect; but these seems like a crude sticking-plaster solution to a complicated game mechanic that really needed a more well-thought-out solution.
As an aggressive builder, I hate putting effort into conquering enemy cities, looking forward to reshaping them to my own needs, preserving as much as I can during invasion (e.g. refraining from using too much aerial bombardment), and then, in the moment of victory, finding that that size-10 city I've finally conquered is a pile of crap.
I really like the idea posted further up, that it should be possible to reduce corruption by simply paying attention to your cities and managing them properly. Trouble is how a computer game can detect "attention". Simply opening the City Screen isn't a good measure. How about getting "anti-corruption" points by:
- Avoiding Civil Disorder. Corruption in a particular city would spike upwards following a civil disorder event, and take a while to subside.
- Building culture buildings in the city. Something like the "tourism" effect of established, old culture buildings.
- Making sure your empire is connected by roads/railways/harbors.
- Avoiding the "Growth in 9999 turns" scenario, either by building the required Aqueduct/Hospital, or by delaying it and managing production in the mean time so that excess food isn't being thrown away?
- In a similar way, avoiding throwing away shields by switching production?
These factors would have to be well-balanced and factored for this to work. I think corruption is a good idea, it's just way out of whack in Civ3, and impossible to minimise by clever, attentive playing. Courthouses are just pathetic in their effect. How about a sliding-scale Courthouse, whose price depends on how effective you want it to be (a bit like the choices of "style" of espionage mission)? Or a late-industrial/early-modern era tech that reduces corruption? (I don't know, the Select Committee or something! That's UK-terminology, maybe the US equivalent would be the Grand Jury investigation or something? Not that I'm saying our UK Select Committees are actually much good at reducing corruption

- but that's off-topic!).