search for "seven climbs of death"
If you don't like the sound of that, Black Moshannon is a really nice ride, 35 miles round trip from the airport, 5000 feet of climbing.
Those are actually two very nice rides, but if you aren't up for that kind of thing I can second SAyre Kulp's suggestions above. Also, the Tadpole loop is a big favorite. After work, we usually go out past the airport, and ride back on Rock Road through Fisherman's Paradise.
Which end of town will you be on? If you are on the Boalsburg end, recommendations might be a little different. PA Bike route G is used as part of a lot of rides.