Hey NickG,
For a small mountain within 3 hours Jiminy Peak is a good one. I live in NJ as well and have been to Hunter, Belleayre, Plattekill, Windham, and Jiminy Peak. All of which are relatively small mountains located within 3 hours of northern NJ (I live in Vernon NJ so maybe a little further for you) All five are good but out of all those I would suggest Jiminy Peak. It has nice wide trails that have a good pitch to them. I have ridden the other 4 for over 20 years and Jiminy only once last year. I will definitely be making more trips back to Jiminy over the other four named above.
If you are looking for some long cruisers with lots of vertical drop make the trip up to Whiteface in NY. By far the steepest and longest vertical in the east. Whiteface also has some Long cruisers. Just make sure the snow is good before committing. It can get icy. There is a lot to do off slope in the town of mirror lake. Lots of amenities. You can stay at cheap bed and breakfast. Just look on-line.
Good Luck
Jt