All the professions need help or materials from the other professions for some of their stuff. Like enchanters need the rod that blacksmiths make to get the "runed" version, or engineers getting the Inlaid Mithril Cylinder plans that blacksmiths need.
Leather is still tough for me to buy at AH prices, but then again, everything is priced pretty high. It's always a tough decision to wait for a guild skinner, or get what I need right now.
If your character is not too far along in levels, start another one who skins or herbs, or whatever else you might be interested in. Even if you don't have time to get them up to the same level as your main character, they can at least help you get more cash with the stuff they sell.