You can take a Northeast Corridor train from Penn Station Manhattan (34th Street) to Secaucus Junction and then change to a direct link train straight to the Meadowlands. This link just opened last fall and it's great. Here is the announcement and specifics:
http://www.njtransit.com/tm/tm_servl...ELEASE_ID=2534
Service to Meadowlands Sports Complex
Updated 4/21/10
Rail service to the Meadowlands operates for major stadium events only.
Rail service will operate for the following major events at New Meadowlands Stadium.
DATE TIME EVENT
Wednesday, May 26, 2010 7:00 PM Bon Jovi
Thursday, May 27, 2010 7:00 PM Bon Jovi
Saturday, May 29, 2010 7:00 PM Bon Jovi
There are also buses that leave from the Port Authority Bus Terminal (41st Street & 8th Ave) and will go there also.
http://www.njtransit.com/sf/sf_servl...edulesP2PFrom#