Yes another one for the d5100 over the d90 or the 60d.
I don't recommend second hand. Sensor tech moves very fast and iso performance has massively improved since the d200.
Have a look at dxomark they rate ever sensor on the market. You can adjust your search fields to the right of the page just to aps-c and aps-c 1.4.
http://www.dxomark.com/index.php/Cam...Sensor-Ratings