I tried sharing this here once before, and it never caught fire... but I'll give another shot.
If you like Settler and Carcassonne, have a look at this website:
http://games.asobrain.com/
Their renderings of both games are very good, the multiplayer play works well and there are plenty of opponents, and even the AI isn't horrid. I wouldn't suggest it's perfect, but it's free to register and play, and not a bad time-killer overall.