J/Boats (of course): http://jboats.com/
J40 Sailors Forum: http://groups.yahoo.com/group/J40Sailors/
J/4x owners page: https://groups.google.com/forum/#!forum/j4x-owners-group
Rod Johnstone’s J/Boats Race Rating Guide: http://www.jboats.com/sailboat-phrf-handicap.htm
Waterline Systems (prev – Pearson Marine Group, prev – TPI): http://www.waterlinesystems.com/
Jeff & Raine’s (J40) Adventure: http://www.j40.org/
Sailnet – voyaging J40’s: http://www.sailnet.com/forums/boat-review-purchase-forum/10846-j-40-long-distance-cruising.html
– Note: the above link is really interesting if you are considering the J40 for very long distance cruising – a good read.
J/Gear – Hats, shirts, etc. http://jgear.vsport.biz/