Where are good places to hike within a few hours of Newark, NJ?

Palisades Interstate Park
its about a 30-45 minute drive from newark
i have been there twice and have loved it
http://www.purdes.com/njhiking/palisades/index.html
http://www.njpalisades.org/

The Delaware Water Gap. Haven't been there in years, but I remember it being beautiful...
http://www.nps.gov/dewa/

Delaware Water Gap is beautiful, as occ says. Serene forests, lakes and water. There's also a cool little trail with great bird wildlife south of Newark. It's a state Wildlife Refuge, but I can't remember the name, near Madison. Finally, you should definitely go down to Cape May at some point.

I agree with Cape May but your main objective should be to get out of Newark asap!

The Environmental Education Center at Lord Stirling Park. 8 miles of trails, a third of which are boardwalk.