We visited Rickett’s Glen a couple years ago and loved it. The Ganoga Falls trails were brilliant, and there was a beautiful beach hidden there as well.
Ohiopyle has some beautiful falls. The river’s great to look at, even if you aren’t doing any rafting or kayaking and Ohiopyle itself is a fun little town.
Make time for Cucumber Falls and the Natural Waterslides.
Besides Ohiopyle, have you gone to the Delaware Water Gap (Bushkill Falls are in the same area)? The Lehigh Gorge? There’s also Hickory Run State Park. Traversing a boulder field is always a lot of fun.
In the area, I’d especially recommend either the Bear Run Nature Reserve. There are several hundred acres of wood and trails that surrounds Frank Lloyd Wright’s Falling Water house and the Fern Cliff Natural Area.
The latter is pretty small, but has many great views of the river.
Laurel Ridge State Park is also a good series of trails. The benefit to it is that pretty much every west-east road through the southern half of the state passes through it and have trail access. Good trails, many nice views.
Conemaugh Lake is one that doesn’t get a lot of press, but is really cool. An combination of trails and an old rail right of way cross a series of oxbow bends in the Conemaugh River Lake. The views are incredible.
Similar can be found up around Kinzua Lake near the NY border.