I have been to these parks and have somewhat ranked from best to worst overall.
Cedar Point - top of the line park, however not best option if kids are under 48"
Busch Gardens Europe - beautiful park with great rides, nice themed regions
King's Island - good variety of rides, may be best option if kids are under 48"
Holiday World (Santa Claus IN) - Free soft drinks, free parking, nice theme areas with waterpark, great clean park
HersheyPark (Hershey PA) - has expanded with new water areas, great variety of rides
Kennywood (Pittsburgh PA) - good variety of rides but park seemed dirty last trip(2008), traditional park
Knoebel's (Elysburg PA) - went this year and was not too impressed; free admission, abundance of rides, GREAT food, but location was near nothing and workers were unfriendly locals, traditional park
Idlewild Park (Ligonier PA) - great for younger children w/ Mr Roger's and Storybook Forest areas
Dutch Wonderland (Lancaster PA) - great for younger children w/ many kiddy rides
Six Flags Kentucky Kingdom (Louisville KY) - located on Kentucky State Fairgrounds, not exactly a beautiful park but many Looney Toons themed rides in Kiddyland, waterpark available
Camden Park (Huntington WV) - traditional park w/older rides, good for under 48" crowd
Lake Winnepesaukah (Rossville GA) - traditional park w/older limited rides, concerts offered on Sunday evenings