http://www.landisenterprises.com/limo/
I have used Landis Limo (5-6 miles north of downtown Lancaster) to go to Phila Pa airport and it was worth it. It was a private car (Lincoln Continental) and they went from my front door to the terminal and when I returned they were waiting with a sign with my name on it for the return home.
Total cost about $175 (1.5 hr drive).

Newark is about the same time although a bit further, but I am sure they can give you a quote. I am probably going to use them for our family (6 people) when we fly in the Spring 2008 to go international.
See the above link for their phone #.