We camped at Bon Echo, but it was a few years back, very, very nice. If you want to head towards Ottawa (Perth), there is Murphy's Point
http://www.ontarioparks.com/english/murp.html, a little inconvenient to get to but some nice trials to walk your dog.
There is also Sharbot Lake which is very nice.
http://www.ontarioparks.com/english/shar.html#which is north of Kingston. at hwy 7. There is another park not too far from Sharbot lake, but can't remember the name of it.
Sandbanks I think is a little crowed to me anyways.
Charleston is our favourite.