depends on realms
items i flip fairly quickly when xfering tcgs for items.
(NOTE: This is based off of my normal realms I buy/sell on)
Medallions/Champions (1.5-3k profit per / 2-5k profit per)
Huge Ogre Cache (500-1k profit per)
Rapid Minds (1-3k profit per)
Teebu's Longblade (5-20k profit per)
Blade of Wizzardry (5-20k profit per)
Sealed Tomes (If using guildbank method) (15-20k profit per) (Unique)
Volatiles -All but earth
Truegolds
Flasks of winds/titanics (Herbs for both)
Felblight
Toys
Transmogs - Glorious
Living Steel/Golden Lotus/Trillium/Harmony
Essences
AH Parts
There's more items out there. This is just a small example.
With the new xp coming up, it might be hard to determine what your profits will be. A lot of people will be dumping.
Best advice is to scout the realms first before doing any purchasing.
(People also offer gold swap services to eliminate the hassle of transferring)