this doesn't occur all that much, but occasionally I do end up with a city that I *really* don't want. Examples of these would be cities that have flipped towards me but which just happen to be in the way, taking up maintenance costs in the process. I might want the special resources that city was taking up, but the city itself really isn't all that interesting. What I do in these cases is give, or even better, trade the city to an AI opponent who I otherwise don't really have to deal with, preferably one a long distance away. Right after that's done I declare war on said opponent and hit the city with a unit that was already 2 squares away from the city and pillage it. City's gone, and you get a reward first in the form of a trade, and another one in the form of the cash you get for pillaging the city. It's a cheesy thing to do, and the AI opponent will definitely resent you for it but hey, if you can afford to get picky about which cities you want to keep what's one more angry AI opponent? 
Oh, and if you want to make even more money...surround the city by cottages, and pillage those before pillaging...it takes some time, but can be quite profitable.
Oh, and if you want to make even more money...surround the city by cottages, and pillage those before pillaging...it takes some time, but can be quite profitable.
