You can post examples and I will try to update as well, but a few of my favorites.
Almost anything with int or dex listed at normal prices.
Examples:
High magic find gear or gold find gear that people have listed at normal prices for those stats, that also have high dex or int stats. Sometimes you can pick up an item for a few hundred thousand that can sell for several million simply because people don't know how to price it.
The same can be said for legendary items. Lacuni Prowlers, andariel's visage, and so many more will be listed for around the lowest selling price of the item because people don't realize that the price for int or dex ones are different. This can also be said for magic find gear. A lot of people don't like to swap +mf, so the gear they want is more expensive because it has good stats +mf, and a lot of times people price based on the stats, but ignore magic find which can make the gear several times more valuable.