Angelique Butler in Dalaran is the First Aid Supplies vendor. Her wares include two very interesting shirts: Wound Dressing and Antiseptic-Soaked Dressing.
Both look like bandages wrapped around your torso and arms, though the Antiseptic-Soaked looks like bloody bandages. Lots of fun. :)
There's also a shirt vendor in the center of Dalaran called Karadonna. She has a nice little screen behind her if you don't want to strip your character down in full view of the door while you try on shirts. Her shirts are elegant blood-elf-inspired creations and very expensive.
- Filigreed Doublet: Long-sleeved shirt with elegant embroidery details available in different colors.
- Filigreed Shirt: Short-sleeved shirt with elegant embroidery details available in different colors.
- Martial: Just like the orange martial shirt, but in new colors.