Sorry, What you are asking is very hard to answer! An idea of what level leatherworker and specialization, if any, would really help. The most profitable items are rare pattern drops, mostly at level 300 skill. Some of the highest volume selling items are leather patches. Each server is different on what is the "HOT" item and they sometimes change from day to day. Sorry to say, but the only way you will make money(and you can make tons of it) is to reseach your server's AH, yourself!
Items I have made for profit;
Armor kits
Earthen leather shoulders
Any Leather headbands
Nightscape items
Gem Studded Belt
Wicked Leather items
Hide of the Wild