The only one worth mentioning is the NBAA website, http://www.nbaa.org
, but you have to work for a member company in order to log in and access the "meaty" parts of the site. I believe that there are a couple of others out there, but they don't compare to the NBAA website so I've never bothered to return to them.
For general education (outside of www.nbaa.org) airliners.net is hard to beat. There are a lot of very knowlegable pilots who frequent this forum - and a few of them fly airliners.
If you're interested in looking for a job, probably the best website out there is http://www.pilotpointer.com
They group all of the major aviation job search sites in one place.
Hope this helps.