LEVEL 80. Cape Hanger - Though this thing might seem useless in fact it is often quite helpful. Putting skill capes that RS gold offer teleportation (like Crafting one) on Cape Hanger can give you additional teleports in your house within the reach of a single right click.

LEVEL 90+. Occult Altar - Occult Altar lets players alter spellbooks with one click. You may select from every magic type which you've unlocked. This is quite handy as changing it with routine method takes some time. Or it's possible to build small altars at level 80 which will let you change into just one magic kind.

LEVEL 91. This is a big money saver but it requires very high Construction level to be constructed.

LEVEL 80. Mounted Coins - Apart from being amusing this one is nearly entirely useless. If you are willing to devote 100mil gold you can have it showcased on cheap RuneScape gold your POH. There is only 1 drawback to owning this thing - you need to shed 100mil gold in order to build it.